What do the letters in circles mean on this drawing?

jimbo84 · 2026-02-12T14:46:49+0000

I have these plans and next to some of the dimensions are letters in circles. eg, C, P, B, S.

What do they mean? A google search hasn’t helped.

bricol · 2026-02-12T14:57:58+0000

I have seen letters used to signify tolerance/fits. but in this case I wonder if it's to indicate a method of joining - solder, weld, press etc - if only you had a key of symbols used on the the drawing.

jimbo84 · 2026-02-12T15:11:39+0000

Yeah a key would have been helpful.

It’s the beam of a steam engine so I wonder if C would represent clearance because it pivots at those points.

Erie Fred · 2026-02-12T15:23:06+0000

Yes, it looks like "ream after fitting for clearance" and the others with an R might be to peen the end of the pin over to retain.

dieselsamurai · 2026-02-12T15:25:09+0000

might be useful

dieselsamurai · 2026-02-12T15:29:06+0000

Also

Help reading blueprint for Twin Wobler model steam engine. C,S,P, & F?

Hey guys, I'm finally caught up with enough my real work that I've got time to play with my mill and lathe. I have been wanting to try to make a small steam engine for a while and this plan that I found online looks easy enough and promising...

www.practicalmachinist.com