Help with antique "pocket blockers" or converters.?

I have recently came into possession of a set of "pocket blockers" (I'm at a loss as to what they are called) IE 6 cast iron & rubber devices which fill the pockets on a regular table to convert it to a carom or billiards table. Basically, they are a K66 style rubber attached to a cast iron device which clamps into the pocket using a hook over the pocket iron & a tensioning device which pull them tight into the pocket. I want to know what they are properly called & any history you know or a reference to antique equipment of this type