A rather strange tap, NOT what I expected

[reggie_obe]

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..

You might be, I have a Greenfield Small Tools #35.
It has tables for BS, BA and French and International, NC, NF and Machine Screw, nothing in those references for 1/4 18 SB that I've found

[reggie_obe]

Dormer on line: https://www.sbsimpson.com/dormer-e71...tools-20-01151
Seems to be a lamp or lighting thread. https://shop.thehouseoflights.com/sw...8-s-b-90-2329/

[J Tiers]

Makes you wonder what they could have wanted that a 1/4-20 could not do. Unless of course, it is so old that there were no accepted standards.

I can see going finer in thread, but coarser is odd. There are lots of reasons for a finer thread.

Reggie: those are pipe size threads, much bigger than this tap, which is not "1/4" size", but ACTUALLY 1/4" in diameter.

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.

And the bore is usually not actually the size it says, since it varies with the "weight" of the pipe. Those grease fittings are pipe thread, and so way larger than the tap. (the last one does not say NPT)

On the side the text is "GT&D CORPN", which would be Greenfield Tap and Die Corporation. That's an older form of abbreviation (Corpn) so the tap may be fairly old, maybe from the 1920s, maybe older. It would be written as "Corp'n" but they left out the apostrophe for stamping. A US company, and not known for making rough and unfinished products.

[dalee100]

While is certainly a new one on me too, I would bet it's a size some manufacturer used to make sure you bought parts from them and them alone. And then it caught on with others to ensure the same idea. I could see this as a "gunsmith" tap. British gun makers often enjoy using silly thread sizes just because they could. But I can't recall any such sizes on a gun I've worked on myself.

It seems it's just common enough to have special taps made, but not so common to have everyone using it. Thanks for sharing J Tiers!

[BCRider]

Dormer on line: https://www.sbsimpson.com/dormer-e71...tools-20-01151
Seems to be a lamp or lighting thread. https://shop.thehouseoflights.com/sw...8-s-b-90-2329/

Look at the picture of the tap and the picture of the lamp fitting. From the pictures in the links clearly both of the threads are bigger than the 1/4" true size of JT's mystery tap. So that's not it either. I'd have to check my spare lamp fixture bits and pieces but if the usual tubular fittings found on the lighting fixtures are 18tpi then it's a different thread again intended for use on 1/4' ID tubing with a bigger OD.

Nice find and a real brain teaser.

If it's fairly old I wonder if it could be a carry over from the early 1900's when there were more 1/4" thread sizes around? Maybe no new product due to the UNC and UNF standard sizes. But companies would still be making things like taps and dies to allow older equipment to still be serviced and used. If this tap is that old perhaps it was one of the last of its type?

[old mart]

I have a box full of taps sorted out from the many legacies given to the museum over the years. There are about 100 odd size taps which have to be kept separate from the standard sizes for fear somebody will use one in error and mess up the job. The most dangerous aren't the weird specials, but the seemingly standard taps with something like +0.005 on them. If I cannot identify a tap, it will normally get binned.

[reggie_obe]

Found iit n my 1935 Greenfield catalog ; SB indicating manufacturers standard stove bolt thread

[mickeyf]

Got no Land Rover and it's breakin' my heart, but I got a 1/4-18 tap and that's a start!

There are certainly straight pipe taps. I have a couple of dozen NOS 1/2-14's that I'd be happy to trade for things that are more useful to me, but they don't seem to be a big demand item.

[eKretz]

Found iit n my 1935 Greenfield catalog ; SB indicating manufacturers standard stove bolt thread

Nice, I thought that might be it. Stove bolt is pretty much just saying machine screw as far as I know though. I think it's just the old school name. The important bit is the "manufacturers standard." Too many of those to keep track of back then. That's why the UN standards came about.

[J Tiers]

Merriam-Webster:


Definition of stove bolt

: a bolt with a round or flat slotted head and a square nut, resembling a machine screw but usually having coarser threads and used for joining metal part


Yep, coarser than any modern standard 1/4" screw, at least according to my references. Presumably a hold-over from before them persnickety and freedom-limiting standards.

I guess a case like "If I want to make a 18 tpi 1/4" bolt, dang it , I will.... 'n you can't stop me...!!!"

[old mart]

Before standards for threads were thought of, starting with Whitworth, every manufacturer had their own designs. This made it difficult to buy spare parts unless you went back to them.

[RB211]

Probably prior to WW2.

[reggie_obe]

Greenfield catalog i#35 (1935) information

Stove Bolt taps
Standard tap is plug.
Left hand, taper and bottom available as Special.
3/16-24
1/4-18
5/16-18
3/8-16

[754]

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..

[JRouche]

Probably prior to WW2.

Lightning made some taps of that size. These were advertised in this old E Keeling catalog. te catalog doesnt have any tools that are electrified. Old stuff. Mostly boiler type stuff.

So yeah, that tap you have is probably very old.

Neat!! JR