Our washers and cups are all countersunk for use with flat head screws, the 3/8”, 1/2”, and 5/8” are packaged with ten #4 x 1/2” screws and the 7/8” and 1- 1/8” are with six #10 x 5/8” screws. The exterior of the 3/8” cups which have a ribbed outer surface designed to be press fit or glued into a 3/8” x 1/4” deep hole. All measurements given are outside diameter (O.D.) and represent the counter bore to fit the magnets, washers, or cups.