BSP Fittings ??

[Jim]

Hi guys

Can anyone explain how BSP fitting are sized ?? I've got some compressor fittings that have a 1/4" female connector but when I measure the diameter of the 'hole' of thread it looks to be a good 1/2" What exactly is being measured when they say this is a 1/4" fitting.

More specifically I have a spare air tank that has a 1 1/2" 'hole' what size fitting should I get for this ?

Thanks

Jim

[Bob Minchin]

Pipe thread sizes are based on the bore of old style, thick wall iron pipe.

With newer pipe manufacture techniques and different materials etc, it is rare to measure anything 1/2" about 1/2" pipe or fittings.

Look up thread tables for BSP on the web and use these to help identify your threads.

hth

Bob

[Frank Erskine]

Which, of course, makes much more sense than the current method of designating pipes by their outside diameter, since they (normally) carry their contents down the inside :-)

[Bob Mannix]

More a shift of emphasis - when pipe sizes came originally from the requirements of flow calculations, the bore was, of course, important and a fitter would ensure all went together. Now no-one does flow calculations and fitters are less skilled, the external physical size is more convenient.

[david lang]

A 1/4" bsp male thread will have a major diameter of 0.518" so this looks like a 1/4" bsp.

Don't have info for 1.1/2" but if its nearer 1.3/8" its 1" bsp. Next size up would be 1 1/4" bsp at about 1 5/8", but 1 1/4" isn't a common size AFAIK.

Dave

[Set Square]

It's probably one-and-a quarter-inch BSP. This has the following dimensions:

Full diameter of thread: 1.650" Core diameter of thread: 1.534 (which is waht you see if the measure the inside of a female thread) TPI: 11

[Jim]

Thanks to all for the info, checked out a couple of websites and those tables make sense now !

I measured the thread again with a vernier caliper and it's 1.53" so looks like it definitely is a 1 1/4" fitting.

Cheers

Jim