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7/32" X 32 Thread Tap

Dobermann

Hot Rolled
Joined
Jan 2, 2014
Location
North Carolina
I found this tap in a box of misc taps and dies that I got from my father. At first I thought it was a 1/4" X 32 tap which was, I believe, the thread for the spark plug in vintage 1930's spark ignition model airplane engines.

However what the application for a 7/32 X 32 thread might be is beyond me. I'm pretty sure it's not a South Bend thread but I thought perhaps somebody here on the forum might recall what it is/was used for.
 
I found this tap in a box of misc taps and dies that I got from my father. At first I thought it was a 1/4" X 32 tap which was, I believe, the thread for the spark plug in vintage 1930's spark ignition model airplane engines.

However what the application for a 7/32 X 32 thread might be is beyond me. I'm pretty sure it's not a South Bend thread but I thought perhaps somebody here on the forum might recall what it is/was used for.

Singer sewing machine or gun smithing thread? I’ll check Singer threads charts tomorrow
 
No, 7/32nds of an inch. Just a 32nd shy of 1/4" The from 2 feet away you wouldn't be able to tell it from a 1/4 X 28 tap. It's a very, very strange size. I cannot find it listed in Machinery's Handbook but if it was in my father's "misc" taps and dies, it could very well have been from the 1930's. However if you can believe everything that comes up on a Google search, you could buy one of them new today.
 
No, 7/32nds of an inch. Just a 32nd shy of 1/4" The from 2 feet away you wouldn't be able to tell it from a 1/4 X 28 tap. It's a very, very strange size. I cannot find it listed in Machinery's Handbook but if it was in my father's "misc" taps and dies, it could very well have been from the 1930's. However if you can believe everything that comes up on a Google search, you could buy one of them new today.

Yeah, all kinds of strange screw sizes existed prior to standardization. Each manufacturer would make his own screws and nuts to whatever size suited him. Also bolt heads.
 
You'll probably never know, it's essentially trivia.
Ferinstance: What is the thread on a 1910's Pierce-Arrow automobile grease cup?
11/16 x 24. I needed to know that at one point, and bought a couple taps to suit. I'll likely never use them again.
 
A few years ago someone on either this forum or antique machinery needed a #12-50 nurled nut for a Lufkin micrometer anvil. That tap could not be found.
Several schemes were tried, but threads that small are very unforgiving with respect to pitch.I made a tool fron 1/8" square HSS steel,and made a nut with a 49.? pitch by using the feed system and backing the lathe manually while not opening the clutch. It went about 2 turns on to the male thread.The thread had to be exact.Someone else made a 48 from stainless that was worse.
Another person sent me a chart that allowed me to get 50 pitch on my B model workshop lathe using the change gears and a home brew compounding sleeve. That worked. I was even able to use the thread dial.
 
Looking through my many thread charts,I found one labeled "fractional machine screws". It shows a 7/32" machine screw with both 24 and 32 pitch threads.
There is also a "stove bolt" chart with a 7/32" that has 22 pitch thread. I almost forgot lamp fineals 1/4-27 thread. 1/4 -28 nuts will go on them because they are short.
 
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Had heard of the BA screws from reading Model Engineer magazine outtakes on line, didn't know about the constant thread pitch scheme.
Saw the 26 pitch series and it reminded me of that thread being used on 3AT and 3C collets. Have made several drawbars for those and also the 20 pitch 2As on my 13" SBL.
 
Had heard of the BA screws from reading Model Engineer magazine outtakes on line, didn't know about the constant thread pitch scheme.

It was around that point that I began to wonder just how many threads do the British have ??
I have the BA taps also as well as the model engineer taps, the BSW and the BSF taps....
The BA stuff is truly different, with a 47.5 deg angle....

Damn, now I gotta go buy a set of BSB (bicycle) taps.... I knew I forgot something!
 
No telling how many threads the Brits have. When you think you know another pops up.I wonder if there is a fish tail for the 47.5 degree threads. I have several of the 60 deg ones and the witworth 55 degree one, but have not seen a 47.5 degree version in any old catalogs.
 








 
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