6′ 8½″ diam., 22 oval spokes, rectangular inner rim, 4¼″ apparent tread.
Hub 17″ face dia., 3″ out from the tyre, pin between at 13″.

Sources: Swindon drg 96784; Side elevation drg, NRM No GW/664 showing wheel reinforcements, Russell vol. 2 p. 154, drg of 7007 'Great Western'; Haresnape, Collett & Hawksworth Locomotives, p. 29, photo of 5073 'Blenheim Castle'
Photo on web at http://www.warwickshirerailways.com/gwr/gwrls163.htm of 4037 in 1937 with reinforced drivers.

Casting: 63.7 mm tread dia., 58.1 mm i/d., hub 2.4 mm out from the tyre, pin at 10.3 mm.

Casting prices and stock . GWR loco sets, price list

Scan of the castings in sets for a GWR Castle