GCR 2-8-0 8K driving wheels.
(As for the first loco, all others which I have seen have hump rims).

4′ 8″ diam., 14 oval spokes, rectangular inner rim, apparent tread, 4″.
Hub, 16″ face dia.; leading driver, level with tyre, other drivers 1½″ out from the tyre; pin between at 13″.

Casting: 44.45 mm tread dia., 37.3 mm i/d, hub, P239 level with the tyre, P240 1.2 mm out from the tyre. Pin at 10.3 mm.

Sources: Johnson, Locos of the Great Central Railway, 2: 140-1 works drawing.

Casting prices and stock . GC loco sets, price list

Scan of a casting in a set for a GC 2-8-0 8K