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Looking for tube stem rim nut thread dimensions


chistech
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I’m attempting to make up a set of pass through rim nuts/valve stem covers. I turned one out of 3/4” hexagon brass today and thought the thread pitch on the valve stem was 10mm x 1.00 but it turn out that’s not quite right. It seems Schrader used some unique diameters and odd pitches. Unfortunately I’ve been unable to find anywhere on the internet what the correct dimensions and pitch should be. The outside of the valve stem measures .040 and the pitch appears to be 26. I understand that the British used a 7/16 x 26 but the 7/16 is a little too big. It might work just the same but I’m hoping someone can tell me what the true dimensions are. Both Coker and Universal had no idea and couldn’t fit any literature in their tech department. The rim nuts available are for the shorter  18” tube stems and do not fit on my 17” tube stems so I’m making longer ones then having them nickeled. Just need the right tap!😡 Any help would be appreciated.

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10 hours ago, Laughing Coyote said:

thanks for the lead Martin but it's the thread for the valve step cap, not the larger body of the lower valve stem. It too is an odd ball thread.

Edited by chistech (see edit history)
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1 hour ago, cudaman said:

Earlier threads on the MTFCA forum indicate that Model Ts used a Schrader 777 stem with a 13/32 x 28 thread.

 

One thread also states that prior to 1920, a larger stem with 15/32" x 26 threads was available.

 

http://www.mtfca.com/discus/messages/179374/255057.html?1324491609

Thanks Cudaman, I think the 13/32 is correct because as a decimal, it's .40625 which is extremely close  to what my stem measures.  I have to check my stems again for the thread count as I found a specialty tap company and to make things worse, they make a 13/32-26 and a 13/32-28! so I have to double check to make sure.

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Just spoke with a company who makes specialty taps. They are quoting me as it has to be made from a 7/16 four flute tap blank. I might buy two as it's about the same price and see if someone wants to buy one from me. Very hard to find tap. You would think with all the old cars still using newly manufactured tubes with metal stems, the taps would be more easily available.

 

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38 minutes ago, chistech said:

Just spoke with a company who makes specialty taps. They are quoting me as it has to be made from a 7/16 four flute tap blank. I might buy two as it's about the same price and see if someone wants to buy one from me. Very hard to find tap. You would think with all the old cars still using newly manufactured tubes with metal stems, the taps would be more easily available.

 

I've been thinking about your stem cover problem since yesterday (as my 32 Nash wire wheel car is supposed to have those, but a different style)

 

..back in the Autumn, I was trying in vain to look up tubes to fit the NOS covers that I have, and I swear I determined they were 10MM, but I can't recall if it was 1.0 or 1.25, etc pitch.  I sure thought I used a tap to check the NOS stem covers..

 

I start to wonder that if mine are really metric 10MM, is there any chance the repro tubes are made with the wrong dang threads?  All it would take is a bad translation from an American blueprint to a Chinese plant operator?  Just a thought? 

 

I will look a mine today, I want to see if I made a mistake...which is possible.

 

.

 

.

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Hi Frank,

I tapped the brass nut I made 10mm x 1.0 which is close but no cigar to the tube stems. The diameter of the tube stem is .40 which makes it bigger than the 10mm. The 1.0 pitch is close to the 28 tpi but closer to 26 tpi. People all over the internet say that tube stems are metric but they really aren't. They are just really odd threads and diameters like the cap tap and die that's sold on ebay. My homemade rim nut tapped with my 10x1.0 starts on the stem but won't go on much past a complete revolution. The plated nut shown in my pictures says schrader on it but it appears to be a cheap stamped plated item and it has formed threads instead of cut threads. It too shows 10mm x 1.00 threads and refuses to thread onto my stems even though I can't use it because it's too short, I tried. The engineer I spoke with at the business who is quoting me the tap said the 13/32-28 is the correct size for a tube stem and he says it's not a common tap because many don't ask for them anymore. I'm going to double check my stems again as I got 26tpi but I think that I checked my rim nut after I ran the 10mm x 1.00 tap through it. Stupid me!

 

If I get the correct tap and my rim nuts all fit correctly, I was thinking of putting them in a dividing head and milling with a small ball mill down the length of them to give them a more factory look. We'll see how brave I get with my machine work!

Edited by chistech (see edit history)
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46 minutes ago, chistech said:

The plated nut shown in my pictures says schrader on it but it appears to be a cheap stamped plated item and it has formed threads instead of cut threads. It too shows 10mm x 1.00 threads and refuses to thread onto my stems

So if I understand correctly, the original 1930s tubes must have been metric...and...the modern repro tubes are wrong threads? ...more below:

 

DSCN3453.thumb.JPG.7f7e820682829783ae7cf3fb12dc2e00.JPG

 

Above are used Schrader nuts and NOS? Schrader covers.  I can't find a tap in 1.0, but using Vernier and metric pitch gauge shown, I get 12 mm x 1.0 for the cover , and 10 mm x 1.0 on the ID of the nut.   I don't know if I had a tap/die back in Autumn, now I can't find one to verify that it would 100% positive as being metric when new in the early 30s. 

 

So my question or thought is,:  I think the new tubes are now made wrong? Yes/No??  is that what you believe, by going by your older repro nut measurements? 

 

BTW, I never found metal stem/angled stem tubes in 500/525 x18, so I just shelved that issue for the time being

 

.

Edited by F&J (see edit history)
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The covers seem to be metric but the stems should be the 13/32-28. The old stems on the model T’s were that thread. They shouldn’t be metric at all. If you Mike a stem you should measure right around .40. 10mm is under that at .393 or 25/64, 1/64 smaller than the 11/32 tap. It won’t go on and the 1.0 pitch is just slightly off from 28tpi. 

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On 3/20/2021 at 8:35 AM, cudaman said:

R.V. Anderson did a short run of custom Schrader thread taps and dies, you might check with him to see if he has any left:

 

rvmodelt@netsync.net

 

 

Really, that would be great. Thanks for the lead, I'll send him a message. Thanks.

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