Gas connection thread size on gas drier.

Pumpguy · October 2021

Can anyone tell me what is the thread size on the 3/8" pipe gas connection that comes on a gas drier? This is a pipe with what appear to be 3/8" fine parallel threads on the OD.

The book that came with the drier says its 3/8" pipe, but its definitely not common 3/8" MIP.

The store I bought the drier at was able to furnish me with an adapter allowing connecting 3/8" flare on the supply side and a common 1/2 MIP OD and some fine straight looking thread on the ID. This adapter did thread onto the the gas pipe on the drier.

Earlier I tried an adapter from the hardware store that had a common 3/8 FIP thread in the ID and it wouldn't fit. Checked with a 3/8 NPT tap and it went in just fine.

Zman · October 2021

That is a weird one. What brand was the dryer?

mattmia2 · October 2021

Maybe it is a flare fitting or there is already a flare or flex connector adapter on it(not sure what the flex connector is, might just be flare)

Pumpguy · October 2021

The drier is a new Whirlpool, as was the old one, 20 YO. Both made in USA.

In the rush to get the new one bought, delivered, and installed, I removed the old one in preparation for delivery of the new one and take away of the old. I didn't realize there was an adapter on the old one's gas pipe (if there even was one. The old drier came with the house so I didn't install that one.)

When I went to connect the gas flex pipe, it wouldn't thread on. It was only then I discovered I needed an adapter. The manual said 3/8 pipe. Went to hardware store for adapter with 3/8 FIP threads and it wouldn't thread on. Looked through my tools for a 3/8" NPT hex die to re-thread, but don't have one, and neither did any of my local hardware stores. This was on a Saturday. Finally called the store I bought the drier at, sales man said he would check, and called back soon after saying he had the adapter. Said he checked it on another drier on display floor and said it fit.

Well, it did fit, and now my drier is connected and working as it should. Just curious now what thread was on that gas pipe? Didn't have time to go off on a tangent to measure the thread.

I'm thinking it might be BSPP (British Standard Parallel Pipe) threads. I ran into those recently on a smaller fitting.

Anybody have any ideas?

Zman · October 2021

The BSPP was my guess as well. I wonder if you ended up with a valve that was intended for another market.

Pumpguy · October 2021

I just came back from the hardware store getting supplies for another project. While there I think I found, at least in part, the answer to my question.

The store has 2 different 1/2" flare adapters for gas fittings. One has 1/2" MIP and 3/8" FIP threads. The other has 1/2" MIP and 12.7 MM RM threads.

So it appears my new drier has 12.7 MM RM threads on its gas pipe.

Now I'm wondering why such an oddball thread is used? And what is the history and other uses of this thread? Internet search engines provided no answers to these questions.

pecmsg · October 2021

NPT and SAE are the standard used here. Anything else and send it back. It’s probably not UL approved.

Jamie Hall · October 2021

Something is amiss with your thread specifications. You need to specify diameter -- such as 1/2" or 12.7 mm, pitch or whether it's SAE or British Standard fine or coarse or metric, and whether it's tapered or straight. I might note that 12.7 mm is not a standard metric size -- although that happens for be exactly 1/2" and might be any one of the US or Imperial threads...

Pumpguy · October 2021

@pecmsg Its a USA made Whirlpool, so from a safety standpoint I'm sure its fine. Been using Whirlpool gas driers for decades with no safety issues, and this one is the same basic design as my older ones.

@Jamie Hall, regarding the thread spec, all I know is that's the thread size on the package the adapter came in. Time didn't allow me to actually measure the thread OD and pitch.

Searching through Machinery's Handbook under pipe threads I found British Standard Pipe Threads for Pressure-tight Joints. It says for nominal 3/8" pipe, this thread pitch is 19 TPI, but nothing is listed with a 12.7 MM dimension. Normal 3/8" NPT threads are 18 TPI.

If time allows next week, I might just try contacting Whirlpool's engineering dept. and see what they have to say about this.

mattmia2 · October 2021

Zman said:
The BSPP was my guess as well. I wonder if you ended up with a valve that was intended for another market.

Unless whirlpool has changed their design recently, it is a piece of steel pipe with a flange on it that screws to the back panel that curves around to the front with a 90 bent in to it where the valve screws to it inside the appliance.

I feel the installation manual will clear this up.

EBEBRATT-Ed · October 2021

Never seen that not that I have done many driers lately. All the ones I have seen are 3/8 standard IPS.

Maybe Whirlpool makes then that way then ships them with whatever adapter they see in the country it's going to

Gas connection thread size on gas drier.

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