I use the 6" size. It works well. Pulls easily out of the drain to be emptied. The hole size is 1/2 inch. I have not had a drain back up whereever I place these.
The overall dimensions are 8 3/8" x 8 3/8" x 3 1/2". The stainer holes are 1/16" wide but vary in length. Some of the slots are 1 5/8" long (side slots) and others are 9/16" - 7/8" long (bottom slots).