My calipers are not that accurate, but here goes:
Outer dimensions: 18.7 mm, 7.0 mm thick.
Depression on top for screw head: 8 mm wide, 3 mm deep.
Hole: 4 mm wide.
Depression on underside: 10 mm wide. 1 mm deep. Edges are chamfered.
Slot: starts 1.5 mm below the top, 13 mm wide 1.9 mm high.
A real covertec wheel i made from plastic, with a metal washer molded in!
No outer edges are chamfered. The edges around the top disc and slot are somewhat rounded. The bottom edge is sharp, as are the edges around the holes.
I assume you don't care about seamlines and pour spouts...