0.300" & 0.400" 28TPI Tap

Good day,

I have been sorting through a load of taps I have been given and come across these two:

0.300 x 28 TPI

0.400 x 28TPI

I cant find any more info about them and I am drawing a blank looking on the web too. They both have the crows foot mark on them. At first I thought they could be BSCY but there 26TPI across the different diameters. Any help will be much appreciated.

Best regards

Rich.

Greetings, Rich.

Our friend Google just found this for me: **LINK**

https://www.efunda.com/designstandards/screws/screw28un.cfm

MichaelG.

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.

BSP 28 tpi threads come close. Colin

Edited By colin hawes on 27/08/2019 15:42:11

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.

Thank you for the prompt replies. Never heard of 28-UN who knew........ Think that one will be in the "come in handy" section of the tap drawer, never to see the light of day again.

Thanks again.

Rich.

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)

Sorry, yes had heard of UNF, UNC etc but not the constant pitch series. Is there a reference book on all threads? Or is that a daft question? I have a zeus book but that is missing quite a few.

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

Only when it gets to 1/4" and larger, smaller diameters use 32 & 40tpi

Jason

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

Threads! Don't get me started!

When I was working at a research establishment we had equipment from all over the world and the headaches of connecting bits together was unbelievable.

We had a Robertson Guide to Screw Threads book and although it covered everything from 3, an Israeli copy of BSP. to Zs a Hungarian thread of 40mm x 6 tpi.? we still got some connections and fittings that defied logic.

I still have a copy of "The Robertson Guide to World Screw Thread Series Symbols" produced by W. H. A. Robertson and Co. Ltd. Lynton Works. Bedford. England. who made dies and chasers.

A truly wonderful publication with some REALLY strange threads, such as.

Artillerie (French)

British Standard Insulator (Cordeaux)

Sewing Machine 100 (German)

Round 30 degree. (Switzerland)

Bearing Form B (German "Klammergewinde" truly amazing and I don't know how you could make it!

or how about American Aero Thread or Dardelet.

Humans really know how to complicate things.

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.

.

I have to wonder why you find it necessary to pretend to conceal the word ‘bastard’

... Its use is [if I may be excused an apparent contradiction] legitimate in this context.

The word is technically appropriate to non-standard ‘born out of wedlock’ threads

.

Surely; replacing some letters with asterisks does not make the word any more, or any less, polite

< rant over >

MichaelG.

Edited By Michael Gilligan on 25/09/2019 09:10:43

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

And don't forget the good old Bastard files, I've got loads of them

Ian

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

Neil

Just been reminded of a weird thread - Leica Screw Mount lenses (LSM) were 39mm dia x 26tpi whitform - now theres an odd mix if ever there was one.

The USSR simplified it to 39mm dia x 1mm pitch - 23 thou of a mm larger pitch which presumably takes account of any minor threadform variations.

Leica lenses will screw into Russian cameras and Russian lenses into a Leica - I have both here - but there can be other differences as well.

Edited By Nick Clarke 3 on 26/09/2019 18:14:24

.

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

MichaelG.

Michael

Can't find it using LTM or Leica as search terms on this site - have you a reference?

Edited By Nick Clarke 3 on 26/09/2019 18:28:48