Chris the mast step has an 8 inch outside diameter. The aft end of the step is 13/16 inch thick and it tapers to 1 inch thick on the forward end. The side that sits on top of the cabin roof (v-birth) has a 64 inch radius to match the roof. A 4 inch by 1.125 inch slot is centrally located and two 11/32 diameter holes are counter sunk .25 inches deep. The holes are centered and straddle the perpendicular center by 1.5 inched.

I hope this helps, but I really recommend buying the manual from the Ariel Association. It's full of great information,

Grady