At the museum, having had many donations of tools over the years, we have many taps which were made for specific jobs in industry. Many only have factory code numbers and can never be identified, and others which are usable at first glance, have + or – tolerances added, which could be disastrous. My favourites are a set of three 0.7" buttress thread taps, they look wonderful, but I cannot think of a use for them.

In a similar situation to the museum I have see threads used on linen and paper presses and the buttress makes sense, but the 0.7" is surprising.

You probably have heard of UN threads.

UN stands for Unified, and is is the standard US thread standard.

Within that you have UNF (unified fine)

UNC (unified coarse)

UNEF (unified extra fine)

UNS (unified special – custom/non standard UN threads drop into this category)

Richard

The constant pitch threads are just a subset within Unified, as are UNS, the specials. They aren't in common use, but a standard does exist for them.

As you correctly stated earlier, BSCY is also a constant pitch thread at 26 tpi, as is BSB (Brass), which, although also 26 tpi, is confusingly NOT the same as BSCY!

I have a number of reference books I use for for threads – Machinery's Handbook, Kempe's, Newnes, IMechE, but my go to first choice for the most common threads is normally Harold Hall's Metalworker's Data Book, no. 42 in the Workshop Practice series.

Edited By David Standing 1 on 28/08/2019 09:51:57

Jason

You are right, and I should know that, having old British bikes and rebuilding them!

Also, manufacturers sometimes use non-standard, politely called "b*****d", threads so you have to buy only their fittings. Those 28tpi taps may have been examples.

I have an idea the Dardalet thread was developed for a particular type of service, but I don't recall what. Oil-well drill-strings? There is a thread-form designed for them. The Cordeaux insulator thread may be similar to the bottle-thread, one that can be moulded in ceramics or glass, such as in the pottery insulators on the old open telephone wires. I looked it up, and Klammergewinde seems to be a bearing manufacturer's name.

Oh, and who had the bright idea that those common, flanged nuts to standard M-series threads should have their wrong, or non-M-series, A/F sizes to loose tolerances and large draught angles?

'

Some 30 years ago I made a spare connector for the Mendip [Cave] Rescue Organisation's warm-air breathing-kit, used to ward off hypothermia. It uses a CO2 reaction with soda-lime in a heat-exchanger, and the gas is from a pub-trade keg cartridge.

Measuring the original showed metric of a particular pitch; but could I find it, even in any of the comprehensive reference-books at work?

Nothing for it but to screw-cut it… on the only lathe I had then, an E.W. Stringer-made, 2.5" BGSC machine with 1/8"-lead screw and change-wheels in 5s from (I think without going and looking) 25 to 65… I succeeded, but I have no idea if that connector has seen service. Probably not, except perhaps in training sessions, as it was a spare and real casualty rescues are rare.

They are certainly very unusual threads, thought they might be a UN series thread so I had a look in my Engineers and Machinists Reference Table handbook. There is a Unified 28 TPI Thread Series (28UN) and the closest is 5/16" 0.3125".

The handbook is by B.B.Babani and is full of good info for the machinist

Ian

The moderators have no issues with such words being used in their proper contexts – bowdlerisation of engineering terms is not necessary.

Neil

.

There has been some quite robust discussion about this, recently, Nick

MichaelG.

.

Here you go, Nick

**LINK**

MichaelG.

Edited By Michael Gilligan on 26/09/2019 21:49:45