A: I don’t see why not. You want to make sure the leg is the same dimensions or bigger so the castor can be screwed into it
A: No - most office chairs are stem mount. this caster is plate mount.
A: No, the screw holes are not countersunk
A: I used #6 self drilling 1 1/4"
A: The hole for the screw is about 3/16" in diameter. The length of the screw will be determined by the thickness of the material you will be attaching the caster to.
A: not square, 1' in one direction, don't remember other (1&1/2"?).
A: The plates are apx. 1 7/8×1 and it is not square, my Home Depot here in Fresno,CA have different plates on the ones that are showing, I bought all the hardware at Home Depot came home with help of friends and put them on.