3′ 3½″ diam., 31½″ i/d., disc wheel, apparent tread 4″.
Hub 7 1/16″ face dia., 1⅜″ out from the tyre.

Source: direct measurement by Fred Phipps in 2000.

Casting: 31.35 mm tread dia., i/d 24.9 mm., hub 1.1 mm out from the tyre.

Casting prices and stock . BR loco sets, price list

More information on the BR class 21/29, 22 Diesel and a photograph of a made-up kit.