A rather strange tap, NOT what I expected

[J Tiers]

I picked this out of the drawer in the shop, but something seemed wrong about it. Then I spotted the problem, which was certainly not what I would expect to see.

[PStechPaul]

!/4-18 NPT pipe thread is common, but that seems to be a straight tap.

https://military-fasteners.com/screws/hexagon+head+cap+screws/b1821bh031c125n

https://www.tractorbynet.com/forums/build-yourself/285272-1-4-18-thread-machine.html

[J Tiers]

It is a straight tap, and is not in the standard thread series. Probably if I knew what the "SB" was, I would not be so surprised. At 1/4", it ain't "structural bolt" as far as I know.

[epicfail48]

Well, i found out that parallel pipe threads do actually exist, in that size too:

https://www.gewinde-normen.de/en/npsf-pipe-thread.html

But, doubt thats what that tap is

[J Tiers]

Well, i found out that parallel pipe threads do actually exist, in that size too:

https://www.gewinde-normen.de/en/npsf-pipe-thread.html

But, doubt thats what that tap is

You are correct. Ain't no way....

This tap is actually 1/4" diameter..... not "for 1/4 inch pipe", which would be a lot larger.

I did not put in a size reference, sorry, I guess I figured the size of the markings would indicate the diameter, but that is not necessarily a good indication.

As near as I can see, it actually is for 1/4-18 threads. Never heard of that size, and I have a whole compartmented tray of odd size taps and dies used on strange bits of machinery, old machines, etc..

[eKretz]

S.B. might be Stove Bolt. Definitely not a common size, must be pretty old.

[754]

Standard British , I bet....... but now to figure out ..US it BSF or BFC ? What does it Mic at ?
am I the only one that has the DORMER TAP handbook ?
and tapped hundreds of Straight pipe threads ?

Dang it BsP 1/4 is 19 tpi..

[Paul Alciatore]

The 1/4" diameter is the one where I have seen the most non-standard threads. I once saw 1/4-23, would you believe. So 1/4-18 is no surprise to me: just one more to add to the mental collection.

The biggest thing that jumps out to me is the way the thread tapers off from the bottom at the shank end. And the flats at the top of the thread get smaller there. Does the diameter increase in that section? How was that made? Did they roll the thread before cutting the flutes? But that does not explain the increasing fill in the valleys.

Was it cut with a die? Only that seems to make any sense.

?????

[J Tiers]

Taps have been die cut (and dies cut with a tap) as well as being ground, cut, and maybe even rolled. It does look like it was die cut, and then the flutes cut.

[754]

Land Rover track rods tap... Tracy tools sells them..
looked at this.. 0

[J Tiers]

OK, on a land rover, might be any damn thing...... they seem to have gone for the "creativity points" from what I am told. Don't have one, thought about having one a while back.

Land rover forum says it is 11/16-16 though......

[PStechPaul]

The tractorbynet discussion linked above says the 1/4-18 screws were used on some aluminum windows. And the other link shows some military bolts of that size.

[ahidley]

Travers sells them under special taps. $17.90

[Richard P Wilson]

OK, I can read what it says on the front, but theres something else written down the side. What does that say? It looks to have made pretty roughly.

[old mart]

As already mentioned, pipe threads are different from ordinary threads, as the size is the bore of the pipe, not the od of the thread. Over the years there have been all sorts of odd sizes made for specific jobs and not intended at the time to cause confusion 70 years later.