thread size on gas taps.....

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MEHAVEY

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`Anyone know what the thread size is on the Commando gas taps coming off the tank?
 
The fastback tank has a larger thread...3/8" BSP with inserts to reduce back to 1/4" BSP. British Fasteners on the east coast has these tap sizes if you need to clean up the threads.
 
The fastback tank has a larger thread...3/8" BSP with inserts to reduce back to 1/4" BSP. British Fasteners on the east coast has these tap sizes if you need to clean up the threads
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Are you sure? I have three fastback tanks, two badge -type '68's and a NOS '71 and they all take the same petcock as my Roadster and Interstate tanks. No reducing inserts.
 
Hi Ron,

Check where the tap threads in. Should be a hex shape on the brass fitting the tap screws into. That fitting also can be unscrewed and has 3/8" BSPF threads. The reason I know is when I bought my fastback tank it was missing the inserts. I purchased a 3/8" tap to clean up the hole and added the fittings, gluing them in with locktite.
 
Out of curiosity, I pulled the 3 original and 1 reproduction fastback tanks off the shelf and all 4 have 1/4 BSP fittings glassed in. No screw in adapters. Not a big deal either way, as you found you can use inserts.
 
I was looking for a petcock on fleabay earlier today and came across this tidbit: Don't know if it's true, but one website selling parts said the 1/4 BSP thread is the same as 3/8 American pipe thread. The female fittings under the tank are 1/2" diameter openings.
 
Hi Danno,

Just looked up 1/4" British Standard Pipe thread - 19 threads per inch while 3/8" American Standard Pipe thread is 18 TPI. They are not a match.

Sorry,
 
I think 1/2" - 20 is the closest to it and some say it will work in a pinch. I wouldn't. Definitely not 3/8" NPT which is huge. It is 1/4" BSPP (BSP parallel) as opposed to BSPT (BSP tapered). This is also called 1/4 Gas. Threads are 19 turns per inch and taps are available from McMaster-Carr in the US (p/n 8328A22 for $17.15). Their catalog explains all this. I bought one because I use it all the time with a number of tanks and bikes.

Russ
 
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