If you mean for the screws which retain the steam pressure, then steel, and high tensile too. Hexagon socket cap screws would be ideal if the design allows them. Or 'Allen Screws' if you don't want to be particular what you call them.

If other screws then perhaps otherwise, but we need more info, please.

Cheers, Tim

.

What a strange comment, Tim

… I would contest that "Allen" is very particular [being a brand name specific to the inventors of the hexagon socket caphead screw]

[yes, I know … it has "become" a generic term … but it shouldn't be]

MichaelG.

Edited By Michael Gilligan on 27/09/2015 20:20:40

hi david,

definitely not brass. the cylinders are subject to considerable for and aft forces in the frames and you dont want anything working loose.

socket cap head or allen screws are totally wrong for miniature loco work.

i have always used 'fitted' steel BA bolts with gunmetal cylinders. there should be a plain unthreaded portion below the bolt head where the bolt goes through the clearance holes in the frame. often the clearance size specified is far too big for something like cylinder bolts, and also far too big for commercially made bolts which are often undersize on the OD.

i make my own bolts for these sorts of jobs.

cheers,

julian