These rings work with older FN / Browning SA-22 - semi automatic 22 - rifles with a 11mm rail that has been milled into the top of the receiver.  The rail is commonly found on the version with a wheel adjustable (windage) rear sight and on some versions with a rear sight that folds down.

See the image of  the 11mm rail on a Browning SA-22 Belgium made, as you can see it is just under 1/2 inch wide.

Low - 0.350 inch, High - 0.600 inch,  as measured from the contact point at the receiver to the bottom of the ring cradle.