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Original Post (Thread Starter)
by Tigernuts
I know this subject has been raised before but my question has a slightly different angle. The correct thread is 1/8"NPS, but fittings with this thread are proving very hard to find (Demon Tweeks, for example, had never heard of NPS, only NPT, in over 30 years of trading). The reason I'm interested in this is because I'm fitting oil pressure gauges to my project bikes.

The Morgo website offers fittings which are 1/8 BSP. I presume that if anyone buys one of Morgo's oil pressure gauge kits, they come with a BSP fitting. I understand that BSP of this diameter is 28TPI, whereas NPS is 27TPI, but you can cram a BSP fitting into the T140 timing cover successfully(?). If using BSP fittings as a substitute is not the bodge it sounds like to me, that's fine, I'll buy fittings from Morgo. However, if this is the bodge it sounds like, I would prefer to find proper NPS fittings if I can. Can anyone gve a well informed opinion? And if using BSP in NPS is seriously frowned upon, can anyone recommend a retailer that sells NPS right-angle fittings? Thanks.
Liked Replies
by Tigernuts
I will give Morgo a ring n Monday and ask them why they're selling BSP fittings when they are not correct for the application, unless they claim they interchange perfectly.
1 member likes this
by quinten
1/8 nps is the same as 1/8 ip... or 1/8 ips .
( they are both parallel sided , not tapered 27 tpI )

nps > national pipe straight
IP .>.Iron Pipe
IPS iron pipe straight

straight threads are not sealing threads , a gasket or o-ring provides the seal and the threads compress the seal

IP is an American thread standard , allowing interchangeability
for lighting fixtures , from about 1900 .
As an obscure thread
it lives with most of us in our homes without our even knowing it
taps and dies for 1/8 ip are available ( because wall lights , lamps and chandeliers are still being made)
and short lengths 1/8 ip pipe are available at almost every local North American hardware store .
( I don't know about Europe or UK )

[Linked Image from]
1 member likes this
by TR7RVMan
Hi, While it’s possible to screw BSPP 1/4-28 onto the late timing cover, it doesn’t take torque properly without bending the threads. Don’t do it!! I have personally tried.

You are most correct it is very hard to locate 1/4-27 NPS. Many sellers say they have it. But when part arrives, it’s in fact tapered.

I finally gave up & bought tap & die. Made my own fittings. But…. If you make it to nominal diameter, it will bee too tight & not screw in. So you want to measure OD of a proper fitting oil pressure switch & make the OD of your blank the same.

This thread was a bad idea from a replacement parts standpoint.

It is very common thread in lamp parts, like the threaded tin the bulb socket screws onto. But for hydraulics it’s hard to come by in the configurations that are useful to us.

Good luck on your search.
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