Correct dimensions of Picatinny/Weaver base.

[HARPERC]

I find myself stuck in the middle of a project. I bought a Burris Fastfire sight to mount on a Ruger 96/44. The chosen base is the B-Square "rail" designed to fit in the Ruger slots as its not drilled and tapped. I ordered one from OpticsPlanet, and found it would not accommodate the "pin/bar on the Burris sight. Tried the sight in the other Weaver type bases around the house, even took it to Cabelas and the sight fits all the other bases. So I sent it back, and OpticsPlanet replaced it zero fuss. The new base arrived in the mail today, and when I saw the box in the mail I told my son I got a hunch this won't work either. It didn't. So the question is: does anyone know the specs and tolerances for both the slots and the pins of this type of system?
Thanks!