# plumbing nipples with rigid conduit.



## reyamkram (Dec 31, 2013)

Where I work I keep commig across place where there is a mixture of rigde conduit with a plumbing nipples,
and some are in a hazrdous location, where in NFPA 70 or 79, can I find this is violation or unsafe practices.
I do not is see any wiring methods in ch 3 , wher it is ok.

Thank you. for any and all information.


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## bill39 (Sep 4, 2009)

Practically speaking, as long as the plumbing nipple has tapered threads, properly reamed, and is galvanized it will be Ok. 

How it can be determined if it came from the plumbing department or the electrical department would be difficult to prove.


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## reyamkram (Dec 31, 2013)

bill39 said:


> Practically speaking, as long as the plumbing nipple has tapered threads, properly reamed, and is galvanized it will be Ok.
> 
> How it can be determined if it came from the plumbing department or the electrical department would be difficult to prove.


you can see different in to 2 types of pipe.


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## HertzHound (Jan 22, 2019)

I think the only argument could be that black pipe isn’t listed in chapter three. So no uses permitted or not permitted. Otherwise they are the same thread. There is no difference between a galvanized plumbing nipple and an electrical nipple. It’s the couplings and hubs that are different


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## Quickservice (Apr 23, 2020)

bill39 said:


> Practically speaking, as long as the plumbing nipple has tapered threads, properly reamed, and is galvanized it will be Ok.
> 
> How it can be determined if it came from the plumbing department or the electrical department would be difficult to prove.


I was on the supply side for 16 years.. all our nipples looked the same as the plumbing ones.


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## Dennis Alwon (May 9, 2009)

I believe electric threads are tapered while plumbing threads aren't


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## bill39 (Sep 4, 2009)

Dennis Alwon said:


> I believe electric threads are tapered while plumbing threads aren't


I believe electrical threads on pipe are tapered & the threads inside electrical couplings are not tapered. Someone here, please correct me if I’m wrong.


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## splatz (May 23, 2015)

Dennis Alwon said:


> I believe electric threads are tapered while plumbing threads aren't


Plumbing threads are tapered, too (NPT) 



bill39 said:


> I believe electrical threads on pipe are tapered & the threads inside electrical couplings are not tapered. Someone here, please correct me if I’m wrong.


That's right, couplings are NPSM (national pipe straight mechanical) which is for mechanical joining not a watertight seal.


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## Bird dog (Oct 27, 2015)

My understanding was the inside of RMC was smooth, so, the wire isn't damaged. Also, does RIGID make separate electrician & plumber thread dies?


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## paulengr (Oct 8, 2017)

On some female fittings there is a step that is chamfered one the electrical version but not the plumbing version.

At least in PVC the plastic pipe has a UL stamp that is different for electrical use. It’s still schedule 40.

In think you’re thinking if NPST which is straight thread not tapered. Not used in plumbing.


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## Coppersmith (Aug 11, 2017)

Bird dog said:


> My understanding was the inside of RMC was smooth, so, the wire isn't damaged.


This is my understanding as well. I was told the inside of rigid electrical pipe has been reamed so that it is smooth. Plumbing rigid is not reamed and can damage wire pulled through it. I'm assuming this applies to nipples and fittings as well.


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## BillyMac59 (Sep 12, 2019)

I saw this done on a few occasions during my apprenticeship. It's usually the result of p*ss-poor planning or a supposed emergency. Anyway, my journeyman told me to spray the schedule 80 black pipe and the conduit junctions with a flat gray paint (used for touching up panels). From a distance or to the untrained eye, it was hard to see. To be fair, he said if forced to do this, add a ground wire instead of relying of the conduit to serve as ground. Over time, galvanic action will corrode and ultimately break the joint. He wasn't too worried. He knew he'd be in the ground before that happened.


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## MotoGP1199 (Aug 11, 2014)

If they used galvanized plumbing nipples, There will be no way to tell from the outside. The threads and pipe/conduit are the same. Only differences are on the inside. Electrical conduit nipples are supposed to be smooth with the internal weld removed or smoothed out, both should be reamed. Some brands of RMC nipples have a smooth finish on the outside and some don't. Some have an obvious weld that is somewhat smoothed or removed from protruding and some not so much. On longer nipples RMC will have listing stickers, but not all the time.

They both use the same NPT threads on the nipples. Electrical couplers are not tapered to allow the conduit to thread in further for stronger lateral support, but is not water tight like a plumbing/tapered coupler.


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## chriszap (Nov 7, 2019)

Dennis Alwon said:


> I believe electric threads are tapered while plumbing threads aren't


Actually, Pipe is tapered-NPT National Pipe Taper. Electric fittings are straight-NPS National Pipe Straight.


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## MotoGP1199 (Aug 11, 2014)

chriszap said:


> Actually, Pipe is tapered-NPT National Pipe Taper. Electric fittings are straight-NPS National Pipe Straight.


Fittings have straight threads for electrical but conduit and nipples are still NPT


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## annawats (Sep 20, 2021)

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## wiz1997 (Mar 30, 2021)

reyamkram said:


> Where I work I keep commig across place where there is a mixture of rigde conduit with a plumbing nipples,
> and some are in a hazrdous location, where in NFPA 70 or 79, can I find this is violation or unsafe practices.
> I do not is see any wiring methods in ch 3 , wher it is ok.
> 
> Thank you. for any and all information.


Non issue.
Over thinking if just a close nipple.

Pipe or longer nipples might matter.
Insides of conduit and pipe are different.

Electrical has a smooth interior, plumbing has a weld line.


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## 210860 (Apr 12, 2021)

reyamkram said:


> Where I work I keep commig across place where there is a mixture of rigde conduit with a plumbing nipples,
> and some are in a hazrdous location, where in NFPA 70 or 79, can I find this is violation or unsafe practices.
> I do not is see any wiring methods in ch 3 , wher it is ok.
> 
> Thank you. for any and all information.


What your referring to is; Chapter 3/ Article 344

344.6 Listing Requirements. RMC, factory elbows and couplings, and associated fittings shall be listed.

Part III Construction Specifications.
344.100 Construction, RMC shall be made of one of the following:

(1)* *Steel with *_*protective coatings*_.
(2) Aluminum 
(3) Red brass
(4) Stainless steel.

*I've never seen _plumbing pipe w/ protective coating, on inside or the outside of the nipple_.

Hope this helps. Have a safe day..


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## micromind (Aug 11, 2007)

Dell3c said:


> What your referring to is; Chapter 3/ Article 344
> 
> 344.6 Listing Requirements. RMC, factory elbows and couplings, and associated fittings shall be listed.
> 
> ...


The protective coating might be galvanize. I don't know for sure though.


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## just the cowboy (Sep 4, 2013)

Bird dog said:


> My understanding was the inside of RMC was smooth, so, the wire isn't damaged. Also, does RIGID make separate electrician & plumber thread dies?


Yes they make straight threads dies. That is what I was always told to use in our threaders, 2x the cost back then.


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## John Valdes (May 17, 2007)

Dennis Alwon said:


> I believe electric threads are tapered while plumbing threads aren't





Bird dog said:


> My understanding was the inside of RMC was smooth, so, the wire isn't damaged. Also, does RIGID make separate electrician & plumber thread dies?


On rigid jobs I never even thought about this. We were threading pipe all day long with no consideration. I have never seen or heard about the dies being different. 
Also when working in the plants, we used nipples from the supply room. There was no distiction between electrical and plumbing.


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## bill39 (Sep 4, 2009)

The definition of a pipe nipple has a limited length, maybe 24 inches maximum. 

People here worrying about difficulties pulling wire thru a plumbing nipple probably are the same ones wearing a mask driving in their car by themselves.


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## Veteran Sparky (Apr 21, 2021)

Rigid Ferrous Metal Conduit (DYIX) UL Mark ANSI/UL6 is the Listing. (electrical rigid conduit)
Everything has a listing. Refer to the 'white book'.
If NOT listed for electrical, it CANNOT be used for electrical.


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## CAUSA (Apr 3, 2013)

reyamkram said:


> Where I work I keep commig across place where there is a mixture of rigde conduit with a plumbing nipples,
> and some are in a hazrdous location, where in NFPA 70 or 79, can I find this is violation or unsafe practices.
> I do not is see any wiring methods in ch 3 , wher it is ok.
> 
> Thank you. for any and all information.


I know a old post but would like to add a toones worth.

For internal smoothness, I have had electrical nipples with poor reaming and poor finishing internally. I need to build a jig with sand cloth to internally ream the nipple to prevent conductor insulation tearing. So it can work for plumbing nipples or electrical rated nipples.

This is a Segway for the issue of dissimilar metals reacting according to the Galvanic table. 

This is a big issue for keeping bonding, if one has not been run separately. Not to mention for threading structure integrity for explosion proof sections.

For a sound installation. The view point of, how the materials react with each other will benefit the installation and your peace of mind.

So if the materials are too far on the Galvanic chart and they are joined. This is a accident waiting to happen. More so in a hazardous area.

The rule of thumb, 

Electricians: need the piping to be conductive and leak at a regulated controlled rate. No galvanic action destroying the joints made up tight. with smooth interior walls for ease of conductor pulls

Pipe fitters: need the piping to not leak, but cares of conductive properties if spec on plans, for galvanic mitigation. and also no galvanic action destroying the joints made up tight.

So no matter what trade. Check the internal condition of the piping and prepare as required. 

Check threading as well no need to have unnecessary galling because of a bent thread.


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## Dennis Alwon (May 9, 2009)

John Valdes said:


> On rigid jobs I never even thought about this. We were threading pipe all day long with no consideration. I have never seen or heard about the dies being different.
> Also when working in the plants, we used nipples from the supply room. There was no distiction between electrical and plumbing.



Actually the thread is the same - tapered, but the electrical couplings are straight thread so the conduits will leak. I am guessing that the couplings for plumbing are tapered.


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## John Valdes (May 17, 2007)

Dennis Alwon said:


> Actually the thread is the same - tapered, but the electrical couplings are straight thread so the conduits will leak. I am guessing that the couplings for plumbing are tapered.


Thankfully we don't need to worry about leaks. Cut, thread, install.


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## splatz (May 23, 2015)

This simple topic is comically complicated to me  

Not for nothing but Ridgid does make different dies for electrical conduit, they make NPSM dies that you'd use rather than the NPT dies you'd use for plumbing. I wouldn't worry too much about causing a hazard using tapered dies. 

Tapered male into tapered male you get a lot of mating surface and the seal is going to be very tight, like pressure tight, OK for plumbing, compressed air, etc. 

Straight male into straight male you don't get a seal in the threads. (You might get a seal between a shoulder on the male side and the female part, especially with a gasket or sealing washer.) But conduit isn't really supposed to be water tight, right, that's why you have to use THWN in wet locations / underground inside RMC. 

Tapered male into straight female you get a limited seal between the threads, it might be weather resistant or drip proof, especially with a sealant, but it or something but it won't seal water or air under pressure. 

The real controversy is, is it code compliant to thread a fitting like say an EMT connector into the threads on an LB? 😰


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## MechanicalDVR (Dec 29, 2007)

Bird dog said:


> My understanding was the inside of RMC was smooth, so, the wire isn't damaged. *Also, does RIGID make separate electrician & plumber thread dies?*


Never seen more than just standard NPT (National Pipe Thread) at any supply house. 

You'd have to special order straight dies.


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## CAUSA (Apr 3, 2013)

splatz said:


> This simple topic is comically complicated to me
> 
> Not for nothing but Ridgid does make different dies for electrical conduit, they make NPSM dies that you'd use rather than the NPT dies you'd use for plumbing. I wouldn't worry too much about causing a hazard using tapered dies.
> 
> ...


It has been quite awhile for me to look at a NEC book, so I cannot give you a note for a specific code.

But... yes this is quite the topic. 

In Canada.. for the Canadian CEC. Rule 12-1006 states, to reference ANSI/ASME B1.20.1 for threading pipe and fitting joining. The B1 is the code book for the piping trades.

But depending on the classification of the area or conduit service. There are rules that govern threading engagement depth and when straight threads are allowed and not allowed. 

An example is 3 complete threads for EMT. But in a Class 1 Division 2. 5 complete thread engagement, and has to be NPT minimum no running threads.

Including a pipe threading chart for all the apprentice's for clarification. with a white paper on threading design.

Also a example of a electrical fitting that uses both.


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## Dennis Alwon (May 9, 2009)

The NEC requires tapered threads but the rigid couplings are not tapered.

My understanding is that for high compression type installs like in thermowells you need the straight threads


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## paulengr (Oct 8, 2017)

MechanicalDVR said:


> Never seen more than just standard NPT (National Pipe Thread) at any supply house.
> 
> You'd have to special order straight dies.


Everything I can find in NEC and UL related to conduit except couplings calls for NPT. None of it mentions NPSM and this is the first thread I’ve seen it mentioned. ANSI does have a separate spec for NPSC (couplings) which is strangely NPST but this doesn’t make sense. I have heard conduit is NPST too but UL 6 is pretty clear that this is not the case.

Any ANSI thread is going to leak. Even perfectly mated NPT threads have rounded roots and crests so there is a spiral shaped gap. If you made them seat perfectly you could turn the pipe to get it connected. Plumbers fix this with some sort of filler (pipe dope, tape, anaerobic thread sealants). In hydraulics they use either machined taper threads with a steep angle like 45 degrees or machined gasketed faces with bolts to squeeze the joint together or something similar with the SAE and JIC fittings so it seals with dry threads (no pipe dope). 

With conduit it’s there as physical protection, fault protection, and inadvertently as electromagnetic shielding (I don’t think they thought about this when it started being used). The wiring is suitable for wet locations so conduit sealing isn’t really a factor.

Not buying the rigidity argument. NPT makes it easier to get the connections together with less friction compared to NPST. You have probably noticed it gets progressively tighter. NPST doesn’t act like that. As to mixing the two, bad idea. You’d have a beveled edge up against a straight edge that is quite literally hanging on by a thread. It would be loose and break loose easy.

At best and this is my speculation here I’ll say that nuts are purposely designed so that the threads stretch and deform so they hold better. The deformation is permanent, This is why you aren’t supposed to reuse nuts and bolts. Of course electricians tend to always reuse and mechanics tend to just lose half of them. So maybe a coupling is NPST (NPSC) but we force it on so that it flares open a bit and gives a more rigid connection than if it is NPT? I don’t know for sure and having a hard time finding anything that talks about what the thread specs are.


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## CAUSA (Apr 3, 2013)




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## splatz (May 23, 2015)




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## kb1jb1 (Nov 11, 2017)

Dennis Alwon said:


> The NEC requires tapered threads but the rigid couplings are not tapered.
> 
> My understanding is that for high compression type installs like in thermowells you need the straight threads


Maybe I missed it but it took 30 posts before someone quoted the NEC requirements of a taper when cutting and threading in the field. That was a question on one of my licensing tests. 3/4 inch tapered per foot. NEC 344.28


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## VELOCI3 (Aug 15, 2019)

splatz said:


> Plumbing threads are tapered, too (NPT)
> 
> 
> 
> That's right, couplings are NPSM (national pipe straight mechanical) which is for mechanical joining not a watertight seal.


Which also means if you use a coupling and a chase bushing on both ends to connect a box and/or enclosure, that fitting is not considered to bond. 


Sent from my iPad using Tapatalk


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## splatz (May 23, 2015)

VELOCI3 said:


> Which also means if you use a coupling and a chase bushing on both ends to connect a box and/or enclosure, that fitting is not considered to bond.


I was wrong about the NPSM, I forgot there's an NPSC for couplings that's slightly different, but that wouldn't change what you're saying. But why would that not be good for bonding?


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## HertzHound (Jan 22, 2019)

I don’t think the threads are the issue with it being considered a bond. It’s the fact that you need two locknuts, or a shoulder and a locknut. So an EMT connector would satisfy the rules for bonding over 250v, but a chase nipple into a coupling or LB wouldn’t.


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## VELOCI3 (Aug 15, 2019)

splatz said:


> I was wrong about the NPSM, I forgot there's an NPSC for couplings that's slightly different, but that wouldn't change what you're saying. But why would that not be good for bonding?


Has to do with the product listing of male fittings. They are tested/listed for use with locknuts and not hub type NPS fittings. 


Sent from my iPhone using Tapatalk


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## paulengr (Oct 8, 2017)

splatz said:


> View attachment 158597


So that makes it clear that NPSC is “straight” tapered threads so just another word for NPT, not NPST despite the name and the screwy way they explain it.

Looks like NPST for electrical, or NPSM is just a myth.


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## CAUSA (Apr 3, 2013)

paulengr said:


> So that makes it clear that NPSC is “straight” tapered threads so just another word for NPT, not NPST despite the name and the screwy way they explain it.
> 
> Looks like NPST for electrical, or NPSM is just a myth.


Both NPT and NPS have the same thread angle, shape, and pitch (threads per inch). However, NPT threads are tapered and NPS threads are straight (parallel). Both threads have a 60° included angle and have flat peaks and valleys.


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## MechanicalDVR (Dec 29, 2007)

CAUSA said:


> Both NPT and NPS have the same thread angle, shape, and pitch (threads per inch). However, NPT threads are tapered and NPS threads are straight (parallel). Both threads have a 60° included angle and have flat peaks and valleys.


If you were threading pipe and ran the threader up the pipe past the point you are supposed to stop the first part of the thread will be non-tapered. The last 1" of thread on the pipe will be tapered thread.

Conversely if you tapped a coupling and ran the tap through all the way the thread will be straight, no taper to it.

When you screw two taper threaded pipes into a straight thread coupling the pipes will meet in the middle of the coupling.


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## CAUSA (Apr 3, 2013)

MechanicalDVR said:


> If you were threading pipe and ran the threader up the pipe past the point you are supposed to stop the first part of the thread will be non-tapered. The last 1" of thread on the pipe will be tapered thread.
> 
> Conversely if you tapped a coupling and ran the tap through all the way the thread will be straight, no taper to it.
> 
> When you screw two taper threaded pipes into a straight thread coupling the pipes will meet in the middle of the coupling.


Absolutely,

the sanding things you can do with a forward/reversing threader versus a cheap unit is ime sera le on a project to correct mistake s and keep materials loss to a minimum.
On a related topic but not related to electrical.

All run through couplings are NPS. And not allowed on any flammable gas installations.😎


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## Quickservice (Apr 23, 2020)

John Valdes said:


> On rigid jobs I never even thought about this. We were threading pipe all day long with no consideration. I have never seen or heard about the dies being different.
> Also when working in the plants, we used nipples from the supply room. There was no distiction between electrical and plumbing.


I have used plumbing nipples for years... Never thought a thing about it. The two SH's I worked for stocked plumbing nipples... All the rigid guys never complained.


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## paulengr (Oct 8, 2017)

HertzHound said:


> I think the only argument could be that black pipe isn’t listed in chapter three. So no uses permitted or not permitted. Otherwise they are the same thread. There is no difference between a galvanized plumbing nipple and an electrical nipple. It’s the couplings and hubs that are different


344.6 is very clear. Conduit AND fittings must be Listed and Listing carries intended use. This was added to all raceways in 2002. All wiring must use a method in NEC, although not all must be in a raceway: two common examples are type NMB and type MC or AC. When those types are used inside raceways it is a mechanical support.
.
Not all hazardous location wiring needs to be GRC with fire blocks. In fact ir can be ANY wiring method with intrinsically safe method.


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## splatz (May 23, 2015)

I didn't re-read the original thread, but I thought that electrical conduit was seamed differently so there would be no burrs on the inside of the pipe, plumbing pipe is rougher inside. A lot of plumbing supplies don't stock galvanized steel pipe any more, but I bought some a couple months ago. I wanted to use some pipe just as structural / support material and 1-1/4" galvanized from a plumbing supply I don't have an account with was cheaper than 1-1/4" RMC.


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## HertzHound (Jan 22, 2019)

Lots of times we need galvanized steel sleeves to put in concrete poured walls before they pour. We normally need 6” sleeves for 4” conduit. There’s a fab shop near us that will sell us the pipe, cut it to lengths specified, and give us the leftover scrap if there is any, cheaper than we can get the pipe from a supply house.

The only thing more expensive is if we have to use the steel sleeves with the water stop.


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## tjodorf (8 mo ago)

Coming from industrial refrigeration construction (blast coolers/freezers, penthouse units), we found many times that conduit connectors wouldn't thread into LB's, boxes, etc. We used NPS taps on these items to resolve the problem, same thing on motors. Tapered taps wouldn't work but the straight taps saved us time, frustration, and money from junked fittings.


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