Table vice for a Shapeoko 2 that has a 1" grid drilled into it's bed. The mounting points for this clamp is 1" center to center and made for #6-32 screws. They are meant to be used in pairs with an adjustable length of 3/4" on each jaw, which gives you over an inch total (why you have a 1" grid on the bed).
Companion to 3" clamp: http://www.thingiverse.com/thing:468536
and V-Block: http://www.thingiverse.com/thing:489254