Jim's Conical Primary Mirror...

Conical mirrors are not at all usual. Here's a 12.5" version. They are mounted
on the mirror cell with a simple 1/2" center bolt. Very nice.

Note the conical mirror is thinner at its edge and gets
thicker and heavier at the center. The flat spot, in
the center, is how it settles onto the mirror cell.

Mounting hardware and instructions. Easy!!

The primary mirror in place on the mirror board.

The rear of the mirror board. Rubber feet for putting the
OTA on the ground 

An interesting view of the conical mirror installed on its cell.

The mirror cell on the mirror board. The collimation bolts
are 5/16" with large knobs for easy adjustment.