Curiosity Tap and Die

[Martin KyteParticipant @martinkyte99762]

I bought a 5/8" 26 TPI tap and die the other day and they are both marked 5/8" 26 TPI BSF ? rather than BSB. Doesn't bother me but it is rather curious.

regards Martin

[Martin KyteParticipant @martinkyte99762]

[EmgeeParticipant @emgee]

Martin

They must be something special, thought 5/8" BSF was 14 TPI, strange.

Emgee

[Craig BrownParticipant @craigbrown60096]

I was digging through my BSP taps earlier and found one that was labelled 1/4" 19tpi BSF. It was certainly a BSP tap so maybe the BSF is there to indicate 55 degree angle as opposed to 60?

[Anonymous]

Both BSP and BSF threads are Whitworth, so 55 degrees.

Andrew

[Craig BrownParticipant @craigbrown60096]

What I mean is that if it just had 1/4" 19tpi on it one would find it difficult to determine if it was 55 degree or 60 degree (apart from the fact it's obvious its BSP because of its large size for 1/4" designation and being 19tpi) so put BSF on it to indicate its 55 degree, instead of an NPT or something (although I believe 1/4 NPT is 18tpi). But if your going to label it then why not label it correctly in the first place….who knows

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Andrew Johnston on 20/06/2020 23:01:06:

Both BSP and BSF threads are Whitworth, so 55 degrees.

.

Which leaves us with the real question:

If you want to indicate the thread form … why not mark it Whit. ?

MichaelG.

[Brian MorehenParticipant @brianmorehen85290]

BSF 5/8 14 T.P.I . Brass (B S C) 1/4 to 3/4 all 26 TPI 5/8 26 TPI , Think this used to be B S B , possibly been changed to BSC..

Brian M

[Martin KyteParticipant @martinkyte99762]

Posted by Michael Gilligan on 21/06/2020 08:09:50:

Posted by Andrew Johnston on 20/06/2020 23:01:06:

Both BSP and BSF threads are Whitworth, so 55 degrees.

.

Which leaves us with the real question:

If you want to indicate the thread form … why not mark it Whit. ?

MichaelG.

Exactly what I would have thought. It is British Standard Brass which was what I ordered so I'm happy.

regards Martin

[SillyOldDufferModerator @sillyoldduffer]

BSB certainly is a curiosity – according to Wikipedia, there is no British Standard for it! It's a misnomer.

My 1949 Newnes Engineers Reference calls it 'Standard Brass Thread 55° Whitworth', and – unlike all the other threads listed – doesn't say who set the standard. Looks like an industry convention; "let all threads in brass tube be cut 26tpi in Whitworth Form".

Who knows why Martin's tap and die are labelled BSF? Possibly its because BSB shares many of the same Imperial diameters as BSF. To make a BSB tap, just take ordinary BSF stock and thread it at 26 tpi, job done. Pretty confusing though, sooner or later someone will be baffled by an allegedly BSF tap that wrongly cuts 26tpi!

BSB and BSF are 55° threads, BSC is 60°. For those working on bikes, 5/16" 26tpi BSC is close enough to M8x1.0 to cause accidental interchange problems.

Dave

[HopperParticipant @hopper]

Maybe ask the manufacturer why they did it that way?

[Martin KyteParticipant @martinkyte99762]

Posted by Hopper on 21/06/2020 10:34:20:

Maybe ask the manufacturer why they did it that way?

Nah, I don't think I would bother. As I said just a curiosity and I thought it might amuse a few people.

Now can anyone lend me a 17/64" British Standard Lawnmower taper tap?

;O)

Martin

[Nick Clarke 3Participant @nickclarke3]

Posted by Craig Brown 2 on 20/06/2020 22:32:00:

I was digging through my BSP taps earlier and found one that was labelled 1/4" 19tpi BSF. It was certainly a BSP tap so maybe the BSF is there to indicate 55 degree angle as opposed to 60?

Either a badly punched BSP – or might it be to indicate it is parallel (BSPP) not taper? – just a suggestion.

[larry phelan 1Participant @larryphelan1]

Ours not to reason why just to get on with it !

[Author]

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