Thread: A 12-20 tap & die set

I have seen that thread table on David Lynch’s site before and wondered in passing as to why there was a mix of English and US threadforms but as I had no need to research them I didn’t take much more than a passing note.

However this thread has intrigued me and I am in a position to confirm or debunk that table; I have about 8 Record bench planes and at least that number of Stanleys so when I next get an hour or so I’ll get the gauges out again and see if I can find a BSW thread anywhere. Most of my Stanley planes are pre-WW2 but I have a 51, a 50’s English 4-1/2 and an Aus 4C.

Hmm, something odd about that table, folks. He gives 5/16 BSW for the cap-iron screw - no ambiguity about that. But why does he say "whitworth form" for some of the other threads? That to me implies there's something not truly BSW about those threads - either it's BSW ("British standard whitworth") or it's not, surely. And if it's not 'proper' BSW,, then what is it? Prior to WW2 it would've been NC if it was following Ameriacan standards to the letter, I'm fairly certain UNC (Unified national coarse) didn't come into being until WW2 when the Yanks & Brits had to cooperate on making things like aero engines. I've read in more than one place that Record copied the Stanleys so closely originally they even used the American threads, so I would expect the Pre WW2 models to have 60* thread form.

After WW2 is when I think the pictures starts to get murky - they may well have lapsed back to Whitworth thread form at some point, but kept the original pitches (which mostly match anyway). And I read somewhere recently that they have gone metric since the 90s, but don't know if that's true, not having handled a Record younger than late 60s.

So I for one will be most interested to read what the Chief's thread gauges reveal......

Cheers,

Hi Ian.

Whitworth form = whitworth profile but non standard thread tpi as I read it.

Originally Posted by eddie the eagle

........Whitworth form = whitworth profile but non standard thread tpi as I read it.

Ok, thanks Eddie. That makes sense, insofar as it can make sense. Why did Whitworth decide on 55 deg for his thread form?? It seems counter-intuitive to an ignoramus like me (60 is a nice round figure that divides easily into a circle), but no doubt he had some reason. The Poms did seem to like making life difficult for themselves with their measuring & monetary divisions so p'raps it was just maintaining tradition?.....

Cheers,

PS. And it wasn't 'til 1948 that 'Unified' thread standards were agreed on according to Wikipedia, so I had that wrong.

I seem to recall it had something to do with the grades of iron being the most common material; 55 degrees may have resisted threads being stripped better. I'm also pretty sure threading boxes for wooden threads were also traditionally cut at 55 degrees for the same reason regardless of the country of origin.

Now for a real head spin check out BA threads.... 47.5 degree angles; heavily rounded profile almost sinusoidal in shape, numbered in decreasing size from 0 to 22 where the pitch is 90% of the previous diameter... and 0 starts at 6mm! English watchmakers and manufacturers of scientific or high precision machinery used them.

Chief, they go even "blunter" for wood threads. An angle I've seen commonly on old handscrews is 90*. In fact someone lent me a tap with that angle many moons ago (I'm pretty sure it was British-made) & I made a few things with it.

It's approx 4tpi & 7/8" major diameter. The "flat" thread looks odd beside the 60 degree form that most of my taps produce (the screw at the front is 7/8" 6tpi & 60* thread form):
90&60 threadform.jpg

Seems to work well enough - the clamps are >30 yrs old & have seen a lot of use, but the threads look in near-new condition.
:)
Cheers,

Originally Posted by Chief Tiff

I have seen that thread table on David Lynch’s site before and wondered in passing as to why there was a mix of English and US threadforms but as I had no need to research them I didn’t take much more than a passing note.

However this thread has intrigued me and I am in a position to confirm or debunk that table; I have about 8 Record bench planes and at least that number of Stanleys so when I next get an hour or so I’ll get the gauges out again and see if I can find a BSW thread anywhere. Most of my Stanley planes are pre-WW2 but I have a 51, a 50’s English 4-1/2 and an Aus 4C.

Picked planes that were old and checked threadformwith a thread gauge..

Stanley 51 rear knob small round head slotted machine screw. Hard to tell. Prob 20tpi UNC however might be 20tpi whitworth.
Stanley 112 front know. 20 tpi unc
Stanley 112 rear handle, 20 tpi unc
Record 10 1/2 post war - UNC.

Thanks for the check.

[Edit] had confirmation overnight. Whitworth thread, but the stanley male threads are rolled and corrosion means that either work. Will keep the order Whitworth. I reckon the 1960s record is UNC.

I'll pm you both the response I got.

A

Well, it took a bit longer than I intended but the results are in.

To summarise;

• US Stanleys used 60 degree threadforms (UN or AN)
• UK and Aus Stanleys used 55 degree threadforms (Whit)
• Records mostly used Whit; BUT there appears to be a short period where UN threads were in vogue....

In the end I only bothered with checking the frog securing screws, the handle and knob studs and the lever cap screws as these were easy to get to and crucially two of them are the odd 12-20 size that sparked off this and several other threads.

US Stanleys:

• Late 19th/early 20th century 66 beading tool
• Type 11 number 5
• Sweetheart era 3,
• Sweetheart era 10-1/2
• Post WW2 51

UK/Aus Stanleys:

• 1950's 4-1/2 (UK)
• 1970's 4C (Aus)

Records:

• Pre-WW2 05-1/2
• Pre-WW2 04
• 1952-1955 04
• 1952-1955 06
• 1952-1955 04-1/2SS
• 1957-1967 010-1/2
• 1979 04 (ex-MOD and date stamped)

The Records were the strangest because the 1952-1955 04 and the 010-1/2 appear to use American threads. The round-topped frog ceased production in '57 and the ogee-frogged 010-1/2 ceased production in 1967 so there may have been a short period in the 50's where American threads were in use. If so then it couldn't have lasted long.

Despite using my 6X head magnifier, strong light and quality gauges I cannot be 100% certain that my findings above are correct; they were originally manufactured to somewhat generous tolerances and some of the fasteners I looked at are over 100 years old with all of them showing evidence of age and sometimes wear. The studs holding the handles were the worst to inspect as they had the poorest quality of manufacture and were also subject to the most damage in use; every rear handle stud had the end threads slightly stretched where they had been fitted into the base castings. I'll settle for 99% though.

There are those who say that 1/4" and smaller threads are pretty much interchangeable; despite this being a nails-down-blackboard statement if your tolerances are questionable enough then for light applications it can be tolerable. I can confirm that experimentally swapping fasteners between planes as part of this research didn't cause me too many cringe moments; the handle studs are so sloppy neither threadform made any difference!
So in conclusion I would say that for plane restoration purposes it is unlikely that mixing threadforms will cause issues. I would attempt to buy the correct threading tools for the expected threadform but either will work to get the tools back into working condition.

Originally Posted by Chief Tiff

Well, it took a bit longer than I intended but the results are in.

To summarise;

• US Stanleys used 60 degree threadforms (UN or UN)
• UK and Aus Stanleys used 55 degree threadforms (Whit)
• Records mostly used Whit; BUT there appears to be a short period where UN threads were in vogue....

In the end I only bothered with checking the frog securing screws, the handle and knob studs and the lever cap screws as these were easy to get to and crucially two of them are the odd 12-20 size that sparked off this and several other threads.

US Stanleys:

• Late 19th/early 20th century 66 beading tool
• Type 11 number 5
• Sweetheart era 3,
• Sweetheart era 10-1/2
• Post WW2 51

UK/Aus Stanleys:

• 1950's 4-1/2 (UK)
• 1970's 4C (Aus)

Records:

• Pre-WW2 05-1/2
• Pre-WW2 04
• 1952-1955 04
• 1952-1955 06
• 1952-1955 04-1/2SS
• 1957-1967 010-1/2
• 1979 04 (ex-MOD and date stamped)

The Records were the strangest because the 1952-1955 04 and the 010-1/2 appear to use American threads. The round-topped frog ceased production in '57 and the ogee-frogged 010-1/2 ceased production in 1967 so there may have been a short period in the 50's where American threads were in use. If so then it couldn't have lasted long.

Despite using my 6X head magnifier, strong light and quality gauges I cannot be 100% certain that my findings above are correct; they were originally manufactured to somewhat generous tolerances and some of the fasteners I looked at are over 100 years old with all of them showing evidence of age and sometimes wear. The studs holding the handles were the worst to inspect as they had the poorest quality of manufacture and were also subject to the most damage in use; every rear handle stud had the end threads slightly stretched where they had been fitted into the base castings. I'll settle for 99% though.

There are those who say that 1/4" and smaller threads are pretty much interchangeable; despite this being a nails-down-blackboard statement if your tolerances are questionable enough then for light applications it can be tolerable. I can confirm that experimentally swapping fasteners between planes as part of this research didn't cause me too many cringe moments; the handle studs are so sloppy neither threadform made any difference!
So in conclusion I would say that for plane restoration purposes it is unlikely that mixing threadforms will cause issues. I would attempt to buy the correct threading tools for the expected threadform but either will work to get the tools back into working condition.

Outstanding Chief. Thanks.

While reading about japanning, I found 12-20 tap and dies for sale (amongst other bailey thread size taps and dies). Not sure if they ship to AUS, but could be worth contacting them.

That's a good quality tap Jk, and exactly what you need for refurbishing planes, but at $76 in our money, plus shipping, you would need to refurbish an awful lot of planes to justify it, methinks!. This mob have HSS taps & dies at a more reasonable price (when they're in stock!), but don't ship to Oz, so you'd need to work through a 3rd party.

The Victornet tap is full-taper but it's a simple matter to convert it to a half-taper or bottoming tap - I just ground a bit off the end of mine...

Cheers,