Ian--have you confirmed your statement above???
Because i just got a set from ken to review for www.6mmbr.com
and the crossbolt is heavy and ROUND--it is not square and should bolt right on to any picatinny style base.
the crossbolt is about .185 in diameter, and pic spec grooves shold be .206, so im pretty sure you are wrong on that one.
please correct me if im wrong though.
BTW--to the original poster, they appear to be a sweet set of rings, but mine wont be on a rifle till early spring.