mystery thread sizes

[Anthony KnightsParticipant @anthonyknights16741]

The tap & die set shown above was given to me by a friend who bought it at a car boot sale. It contains some strange thread sizes which do not seem to fit any of the series I have come across. There is no manufacturers name on any part of it and the case and wrenches appear to be hand made. I list all the sizes below. Can anyone offer any suggestions as to what they were used on.

3/16″ x 32 tpi (BSF ?) 1/4″ x 25 tpi 1/4 x 30 tpi 5/16″ x 26 tpi 3/8″ x 26 tpi

3/8″ x 30 tpi 9/16″ x 20 tpi.

[Anthony KnightsParticipant @anthonyknights16741]

[NJHParticipant @njh]

Well Anthony here’s a starter!

 

5/16 x 26 – BSP

3/16 x 32 – BSF

3/8 x 26 – BSP

 

Cheers

 

Norman

[KWILParticipant @kwil]

Anthony,

 

They all fit in the Brass and Cycle thread ranges .

 

K

[Anthony KnightsParticipant @anthonyknights16741]

Thankyou guys. I am aware of the 26 tpi range. It was the 25 and 30 tpi threads which were puzzeling me.

[Speedy Builder5Participant @speedybuilder5]

loosley speaking, 0Ba is 1/4 x 25 in fact it is 0.236″ major dia x 25.4 pitch (its the only nearest I can find in Machinery’s Screw Thread Book 19th edition circa 1965) and 5/16 x30 tpi could be a BS Cycle pitch, but not a preferred size.

 

Does thread angle help to identify:-

Ba is 47.5 degrees

cycle 60 degrees and

Whit 55 degrees

[JasonBModerator @jasonb]

Tracy have both the 25 & 30tpi threads listed under brass, cycle & special. I think some of the old motorcycles used these pitches.

 

J

[Ian S CParticipant @iansc]

3/16″ 32 TPI is unf. Ian S C

[KWILParticipant @kwil]

Only UNF if it has the correct thread angles! My bet is still on Brass and cycle threads looking at the kit.

[Anthony KnightsParticipant @anthonyknights16741]

Looks like the thread angle is 60 degrees so probably cycle/brass sizes.

Thanks for the replies gentlemen. I now think this kit may have come from

a workshop where they repaired or maybe built cycles and /or motor bikes.

Drifting off thread slightly, is there any particular reason why 26 tpi came to

be the standard thread size used on bikes.

where they repaired or built cycles or motor bikes.

[Roderick JenkinsParticipant @roderickjenkins93242]

Brass thread was a constant pitch series for use on brass tubes used originally, I believe, by instrument makers who could use the same chaser on any diameter. The relatively fine pitch allows a thread to be cut on thin walls. Since bicyles were made from tubing then I guess that the manufacturers adopted a similarly useful size.

 

Rod

[John Stevenson 1Participant @johnstevenson1]

That tap and die set in the first picture is starter set for a cycle mechanic and covers cycle threads BSC formerly known as CEI.

 

This is the full set.

 

 

And fully opened up.

 

 

The large tap is 1.370 [ not 1.375 ] x 20 for the bottom bracket.

 

Taps and dies start at 3/16″ x 32 up to 9/16″ x 20 right hand and left hand for pedals.

 

Also contains weird-o’s like 17/64″ x 26 for cotters [ still used today ]

 

One very useful feature that this type of slip die possesses is that if you have a bumped up thread you open it out, place on the thread lower down, tighten and wind off as they will cut in reverse.

 

Result is it cleans up the thread without fear of getting it cross thread or drunken.

 

I wasn’t fortunate enough to be given mine, I had to buy mine and it cost a whole weeks wages.

 

John S.

[Anthony KnightsParticipant @anthonyknights16741]

Congratulations Mr. Stevenson, the mystery is solved. Unfortunately, I have the apprentices set while you have the Master Mechanics kit. As I got it for free I suppose I can’t complain. Any idea as to the age of this stuff and is it still useable or have bikes gone metric. The phase “If it ain’t broke -don’t fix it” springs to mind.

[John Stevenson 1Participant @johnstevenson1]

I have no idea of the age of them. All taps and die pieces are marked with the sizes but that is all, no other marks.

 

I was told they were made as apprentice pieces but don’t believe that as I have seen other sets identical to mine with identical lettering on as regards fonts.

 

If these were apprentice pieces they would have had some identifying marks on, even if only initials.

 

I still use mine from time to time, often for thread restoration but recently I had to tap some holes out in a vintage carburettor to 1/4″ x 25

 

John S.

[AESParticipant @aes]

Anthony,

QUOTE:

Any idea as to the age of this stuff and is it still useable or have bikes gone metric.

UNQUOTE:

 

Just FWIW Anthony, only a few weeks ago I bought 5 off 16 inch bike wheels, brand new (for a child’s pedal car project that I won’t bore you with now). I live in Switzerland, the wheels are actually for a Japanese folding frame bike, though when they were delivered I saw the rims are stamped “Made in Taiwan” (as are the tyres BTW).

 

Because of all the above I was sure that the threads on the ends of the axles “must” be Metric. Nah! The threads are 5/16 ins (five sixteenths of an inch) x 26 TPI, (CEI) which, after a lot of “web walking” (thanks to Colin Usher in the end) I found out is still pretty much “A” if not “the” standard thread for bikes just about the world over.

 

The local (Swiss) bike bloke told me that apart from some locally made “specials” built in small quantities here, which have Metric threads (usual “F” but not always), most mass-produced bikes still use the British CEI bike threads.

 

So if you’re going to do anything at all with “bike-trickery” (or pedal cars!) in the future then that taps n dies set is definitley NOT going to sit idle on the shelf – in fact can I borrow your 5/16 x 26 TPI die please?!

 

 

Krgds

AES

[Anthony KnightsParticipant @anthonyknights16741]

Hi there AES. You are welcome to pop round and borrow the die you require, but as I live just outside Leeds and you are in Switzerland that may not be as easy to do as it is to write. I was in a car spares shop the other day and noticed some bicycle axle nuts marked 10mm, which lead to the comment regarding metrication of bikes. What the actual thread was, I have no idea.

[AESParticipant @aes]

Anthony,

 

My tongue was very much in my cheek of course!

 

I have got the appropriate die on order (I found the tap in amongst a pile of stuff left to me by my Dad when he died).

 

Still at least you’ll be able to help all the local bike blokes.

 

Cheers

 

AES

[Author]

Posts