Correct thread pitch for the 68 era petcocks?

gtsun

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Sep 21, 2009
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My 68 for 441 shooting star has those brass valve type petcocks. Some people say it's quarter inch NPT but I've seen others say they are quarter inch BSP. Which one is correct and what's the difference?
 
gtsun said:
My 68 for 441 shooting star has those brass valve type petcocks. Some people say it's quarter inch NPT but I've seen others say they are quarter inch BSP. Which one is correct and what's the difference?
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= 1/4" BSP(P) (or '1/4 Gas') which is 0.518" x 19 TPI, 55-degree parallel thread.

BSP
http://www.britishfasteners.com/threads/bsp.html

NPT is a tapered thread. The nearest US equivalent to BSP would be parallel NPS(M) however, thread angle (60 deg.) nominal diameter and TPI (0.540" x 18) are all different to BSPP (however, BSA and Triumph oil pressure switches were 1/8" NPT (early) and 1/8" NPS (later).

NPT
http://www.gewinde-normen.de/en/npt-pipe-thread.html
NPS
http://www.gewinde-normen.de/en/npsm-pipe-thread.html
 
Thanks L.A.B. When I took mine out they are actually 1/8" BSP. Not 1/4". Perhaps the later BSA's had 1/4".
 
gtsun said:
When I took mine out they are actually 1/8" BSP. Not 1/4". Perhaps the later BSA's had 1/4".
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:)


1/4 BSP was the usual size from around 1970. Before then, I believe they did use other sizes, 1/8", 3/8" etc. just to keep things interesting! :wink:
 
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