3′ 6″ diam., 10 oval spokes, rectangular inner rim, apparent tread 4¼″.
Hub 13½″ face dia., ¼″ out from the tyre, pin between at 8½″.

Note: some references give the wheel diameter as 3′ 4″ as in Marston's text. I am accepting 3′ 6″ dia. as in Marston's reproduced weight diagram, and in Hall & Fox, Preserved Locomotives of British Railways (1995). 3′ 6″ implies new tyres+tread overlap of just over 4″ thickness on top of my actual measured internal diameter of 33½″.

Source: preserved loco measured direct at NRM, York.

Casting: 35.0 mm tread dia., 28.0 i/d, hub 0.2 mm out from the tyre, pin at 7.1 mm.

Casting prices and stock . BR loco sets, price list

Full sets information and prototype photographs.