A rather strange tap, NOT what I expected

[Bented]

I feel the same way.

-D

One would think that you should have figured this out in 2006 (-:

[Doozer]

That chart is for STRAIGHT pipe threads. Believe what you want. I give up.

I feel the same way.

-D

[old mart]

That is what I thought about stove bolts, BC.

[BCRider]

Top ad is a tapered threads the other 2 state size as 1/4 in.. one specifically says STRAIGHT Thread..... one has a 3letter designation....

Ya, but it was still a PIPE thread with parallel threading so the body of the threads was still up around the 3/8'ish size of a 1/4" pipe thread. Compare the threads to body size of Jerry's tap to your pictures. Vast difference easily seen just by looking at the pictures of the grease nipples.

As for stove bolts I'm guessing that they were kept fairly coarse because of the heat rusting out the threads faster? So using coarse threads keeps them holding things longer?

[J Tiers]

A 10 tpi thread on a 1/4" screw is pretty goofy. I modeled one up in CAD, and I wonder if it might have been a 2 start thread. The model was pretty strange-looking.

The reason I ask about the 2 starts, is because a standard 10 tpi thread would leave a pretty small core area on a 1/4" diameter, it seems more like a sheet metal type screw than a machine screw

[Willy]

I believe this is an old obsolete auto thread from about a hundred years ago or perhaps a bit more. Back than as we all know there were a lot of obscure threads sizes before standards were set. I have some old automotive fastener catalogues that list not only the 1/4x18 thread size but also 1/4x10 and 1/4x16, plus others too numerous to mention.
Fortunately standards have been in place long enough now that we don't bump into this too often anymore unless doing an old restoration where one needs to keep all aspects 100% original.

Oddly enough MSC still stocks this tap.
https://www.mscdirect.com/product/de...rItem=04840195

[eKretz]

The ¼"-18 thread that is the subject of this thread has nothing to do with pipe thread... It's a plain Jane machine screw thread with ¼" O.D. and 18 threads per inch. ¼" -18 pipe thread is something else altogether. The reasons for the push for standardization of threads way back then are evident even today!

[754]

I did not catch that part m I will go back to read description of what I posted.

[PStechPaul]

That chart is for STRAIGHT pipe threads. Believe what you want. I give up.

[754]

Yes a tapered pipe thread. . I gave an example of 1/4 diameter x 18 tpi grease nipples..

[PStechPaul]

https://www.engineersedge.com/fluid_...eads_13376.htm

1/4-18 is 0.517" to 0.526" major diameter.

[754]

Top ad is a tapered threads the other 2 state size as 1/4 in.. one specifically says STRAIGHT Thread..... one has a 3letter designation....

[reggie_obe]

I found one source for 1/4"-18 hex head bolts, from a military fastener supplier.

Meaningless. At one time, any wholesale fastener company would supply you with any diameter, thread, head, finish, etc. with just a little leed time. It's what screw machine shops were all about.

[PStechPaul]

Did everyone on here MISS it.?.
I showed 3 current suppliers some WELL KNOWN SUPPLIERS... Today of grease nipples in that size... there is one application..
none that probably a lot of us have seen..

Those are 1/4" straight PIPE threads, which are about 3/8" to 1/2" diameter. I found one source for 1/4"-18 hex head bolts, from a military fastener supplier.

[J Tiers]

Lightning made some taps of that size. ........

Yep, 16 (!😶!) 18,20 thru 26, but no 28..... MUST be an old book.