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Correct thread pitch for the 68 era petcocks?

Correct thread pitch for the 68 era petcocks?

Postby gtsun » Sat Aug 27, 2016 9:04 am

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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Re: Correct thread pitch for the 68 era petcocks?

Postby L.A.B. » Sat Aug 27, 2016 12:25 pm

gtsun wrote: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?



= 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
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Re: Correct thread pitch for the 68 era petcocks?

Postby gtsun » Sun Aug 28, 2016 12:07 pm

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".
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Re: Correct thread pitch for the 68 era petcocks?

Postby L.A.B. » Sun Aug 28, 2016 12:19 pm

gtsun wrote:When I took mine out they are actually 1/8" BSP. Not 1/4". Perhaps the later BSA's had 1/4".


:)


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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Re: Correct thread pitch for the 68 era petcocks?

Postby Bob Z. » Tue Aug 30, 2016 10:13 am

If your tank uses the larger 3/8" size fuel tap this adapter is nice and let's you use a wider range of 1/4" taps.
https://www.eurojamb.com/petcock-adapto ... csn3e9plv6

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