A full round capital with an optional square capping piece.  Copied from an original dating from the late 1700’s.  The reduction in price for buying the capital without the capping piece is shown below.

Capital Height (including short protrusion that locates cap):1  3/4 ” (45mm)

Capital Width Top :2  11/16 ”  (67mm)

Capital Width Bottom:2  1/16 ” (53mm)

Internal Diameter  1  7/8: ” (48mm)

Capping Piece Height: 1/4 ” (6mm)

Capping Piece Width: 3 ” (77mm)  and depth is 2  7/8″ (74mm) – see note below:-

NB.  The front face of the capping piece has a shallow curve protruding to a maximum depth of 3″ (77mm)