I marked the location of the 4 bolt holes on the clamps using a #40 drill bit without going all the way through, using the support leg holes that were pre-drilled earlier (I installed the support legs on the plywood base to do this). I did this for both clamps. Drill the clamps for the 4 bolt hole locations for each clamp and counter sunk them from the inside of the clamp. I made sure that the flathead bolt heads are slightly protruding from the clamp so they will not rotate when installed on the jack. Drill out all the holes to #12 on both the support legs and the clamps. Install the support legs on the jack (install the support legs on the clamp bolts then on the plywood base).
