Unusual Thread Type?

Hi All,

Just found about 10 of these taps wrapped in greased paper; I have not seen this WF type before?

Guessing that it is Whitworth Fine; 40 tpi gives one thou per revolution so is it a micrometer thread? Is the .2 1/5 of an inch?

Cheers, Martin

I have an inkling that the WF stands for Whitworth Form.

Andrew

Whitworth fine ????? That,s a new one for me !

40 tpi Whit Form is the basis of of a long established and widely available "Model Engineer", ( ME ) series which ranges from 1/8" to 1/2". Very useful for steam fittings etc. It's not Whitworth "fine".

0.2" dia. would not be in that ME series though. The rather rough etching of the size in the photo might suggest that these examples are specials.

Edited By Clive Brown 1 on 21/08/2023 18:48:04

Those threads look like multi-start to me.

Best regards,

Swarf, Mostly!

The Graces Guide entry for John Harris Tools includes this advert:

Dave

Dave,

interesting advert!

what might be the tapping drill size for a special thread like these?

cheers, Martin

Thread depth for a 40tpi Whitworth thread form is 16 thou. So core diameter is 0.2" minus 32 thou, equals 0168". Say we want 75% thread depth so add 8 thou to the core diameter to get 0.176". Call it a number 16 drill or 4.5mm. In brass I'd probably drop down to 4.4mm. Not a lot of thread to play with!

Andrew

I too assume that WF in this context is probably Whitworth Form, but when Joseph Whitworth came up with his thread dimensions, it wasn't a British Standard, though obviously later became one, along with a fine thread to become BSW & BSF, so perhaps there was a Whitworth Fine before the BS was added.
I can't find when the finer thread form was originally started.
There's an interesting article on The History of Whitworth here, which includes some info on the origin of the spanner sizes.
http://www.team.net/sol/tech/whitworth-hist.html

Interestingly JW himself proposed a thread series based on decimal, rather than fractional, which did include a 0.2" diameter, though that was in 1897, which rather predates those taps by the looks of it.
https://en.wikisource.org/wiki/Miscellaneous_Papers_on_Mechanical_Subjects/A_Paper_on_Standard_Decimal_Measures_of_Length

Bill

Edited By peak4 on 21/08/2023 22:33:38

Many thanks to all for that interesting information.

i am happy to let 4 of these go to forum members if anyone would like one, I’ll do the postage also!

first come first served!

Cheers, Martin

Speaking of odd taps and dies ect, like many others, I suspect, I have ended up with a collection of odd taps and a few dies over the years. Most of them are BSW or BSF, not much call for them these days, but it seems a shame to just dump them, but what does one do when you have six or seven of the same size ? [Dont even ask how this came about ! ] Also have a few number and letter drills, very few know what I ,m talking about if I mention "Letter O " drill

Makes me realize just how old I am. I even remember when we used to use 6" rules !!!!

Voice from the back say,s "What were they for ?"

6" rules for tea stirring of course.

Roy

... and for opening your pay packet!

Nobody want one?

Martin

Very generous offer Martin. We are in your neck of the woods in a week or so. If you have one available shall we pop round and pick one up?

Rik

Martin - I have sent you a PM.

These taps are, I suspect, as used in some BSA gunsight mechanisms.

Rik, no problem, you know where we are?

Oily Rag, will check the PM

martin

Might prove useful ! may I have one , if theres any left. Noel.

Sorry, now all gone!

Martin

One rather lovely Tap arrived safely this morning, Martin

Many thanks

.

MichaelG.