Quote Originally Posted by RP12 View Post
Best thing to do is get a caliper and measure the lug and recess to eliminate that possibility.
The lug height measures 0.288".
The lug recess in the aluminum pillar measures 0.308".
So I have 0.020" (twenty thousandths) clearance, so the lug is not bottoming out.

Therefore I'm still look for the reason that the front screw aluminum pillar area does not touch the bottom of the steel cylindrical receiver even after proper mounting screw torqueing sequence.

I also note that with my caliper I can measure that the front part of the aluminum channel is narrower than the rear. In other words the aluminum extrusion is deflected or warped a bit which could affect the front mount.