Pedal threads - BSP or BSF?

[Amanda P]

I know that bog-standard pedal threads are 9/16", 20 tpi, but is that BSP or BSF?

I'm asking because an engineering friend is making up a set of short cranks (for the diminutive Mrs Uncle Phi's use) by boring out and cutting down a regular set. Boring the holes for the pedal holes is tricky because they have be exactly parallel to the bottom bracket axis, and then the thread has to be cut perfectly square too. He's going to do some clever stuff with lathes and pillar drills to get everything lined up.

Then we need to get some taps. I'd just get Park Tool ones, which presumably will be the right kind of thread, but he uses a more general supplier from whom he can get discounts, being in the trade, and they don't sell these taps as specific bike tools but just general engineering stuff.

So, any of you engineering types know - quick as you like - BSP or BSF? Or is it a silly question?

 

[Profpointy]

if they're 20tpi, I suspect strongly they are neither BSP (British standard pipe) nor BSF.

9/16 BSF would be 16tpi

And not sure if 9/16 is likely to be BSP at all - but BSP are (I think?) listed by pipe size rather than across the threads.

... and found after I'd typed in the above British Standard Cycle thread - which is indeed 9/16 by 20tpi.
(or now red-defined as "ISO 14.2 by 1.27mm, with a slightly different but interchangeable thread form (truncated rather than rounded peaks and valleys)."

see also this thread in the Other Place:

http://forum.ctc.org.uk/viewtopic.php?f=5&t=1078

 

[jazzkat]

I've learnt something there.
I always "knew" BSCy was 26tpi and wasn't aware that the pedals were a different thread form.
What an enlightening place this forum is!

 

[Profpointy]

I've learnt something there.
I always "knew" BSCy was 26tpi and wasn't aware that the pedals were a different thread form.
What an enlightening place this forum is!

presumably BSCy covers a number of sizes, so I'd not be surprised if summat else on the bike is 26tpi.
( my knowledge of BSCy is purely today's googling / Wikipedia, so do check up for yourselves, and ideally use a thread guage too)

 

[jazzkat]

A lot of old british motobikes use 26tpi bsc, which is where I know it from. I'd never heard of different sizes.
Everyday is a school day

 

[Profpointy]

A lot of old british motobikes use 26tpi bsc, which is where I know it from. I'd never heard of different sizes.
Everyday is a school day

well I'd be surprised if every size bolt had the same TPI. Not wholly impossible I suppose, maybe if there were only 3 sizes fairly close together, but would be odd all the same.

 

[jazzkat]

Every cycle thread bolt I've seen on a British motorbike bike (and I've had a few) have all been 26tpi, regardless of their size, which is why I was surprised to see the 20tpi figure.
I never got around to cutting threads on a lathe, a good bit of skill needed for that, especially, as the OP says getting it all square.

 

[wisdom]

Bsp is a slightly tapered thread, to create a tight seal in pipework.there is also a parallel bsp thread but I have only used the tapered type on steam pipes 2"diameter.

 

[Profpointy]

Bsp is a slightly tapered thread, to create a tight seal in pipework.

are you sure? My scuba diving regulators & tank don't seem to have a taper on them - they are DIN fitting, which strange as it may seem is apparently 5/8" BSP

 

[wisdom]

are you sure? My scuba diving regulators & tank don't seem to have a taper on them - they are DIN fitting, which strange as it may seem is apparently 5/8" BSP

Apologies for misleading I have edited my post to mention there is also a paralell bsp thread in my haste I didnt think my answer through.

 

[Profpointy]

Apologies for misleading I have edited my post to mention there is also a paralell bsp thread in my haste I didnt think my answer through.

I have seen tapered threads, perhaps even on some older scuba tanks (where the tank-valve screws into the tank), but think modern ones are straight. Didn't know the tapered threads were also under BSP standards. As someone upthread said, every day's a school day on here