classic motorcycle forum

A metric spec, but clearly not a metric thread.
I read somewhere many years ago that the early US loco's (the ones always featured in Westerns) used Imperial threadforms until US manufacturing and standards caught up.

Learning about various thread forms is one of the great entertainments of ancient machinery (not just motorcycles). In the early days of the automotive industry there were three great centres of industry, USA, UK, and Europe. Of which Europe had several major subsets, France Germany and Italy with activity elsewhere on top of this. None of these areas really spoke to each other. They couldn't, there was only surface post and ships, let alone all the different languages, even friendly and helpful communications took months so all played alone. All had the same problems. All had much the same knowledge base, machinery, metals and men to work with and all invariably came up with much the same answers to their problems but not quite hence the weird mixture we find today.
Everyone has known the need for standardising these things for over a hundred years but we haven't managed it yet and I doubt we ever will. Human beings can be remarkably contrary.
Working on an old motorcycle is just a pleasant way of learning all this history and ain't it fun.

PS
Just be glad you haven't had to dive in to metric stuff. That's another world of mystery all of its own.
   

Interesting conversation with the Guru this afternoon....

I hadn't realised it, but that banjo "post"  fitting has a counterpart in the Pilgrim pump outlet, which is BSP as standard, and the Rocker box fitting is BSC as standard.

Here's photos of the 2 parts from the supplier...





Apart from the machined channel on the upper part.... they're both nigh on identical banjo fittings.  It's quite within the bounds of probablity that the BSP pump outlet part (the lower photo) has been modernised to have the channel cut into it to improve oil flow and that photo is of an older style part, so the parts would look virtually identical when you're just picking them up and throwing them into a package.

So it's quite likely I've just been sent the wrong part...  hey ho, I can easily see a mistake like that happening, we'll see what they say at the suppliers....

BSP confuses everyone. The belief is that it refers to the pipe I/D, but that's likely a myth, too.

1/8" BSP (British Standard Pipe) is 0.383" major diameter, 28 tpi. (There's also BSPT which is a tapered version)

3/8" BSCY (British Standard Cycle) is 0.375" major diameter, 26 tpi.

Both are commonly found on pipe fittings on old British bikes.

Leon