These incredibly versital boards are hugely useful. During the hot, humid NYC summers, we use double screened boards in place of inner covers. Block them up on each end to create air-flow over the hive.The two screens are separated by 1/2" of space, preventing communication through the board. So, they're also useful for overwintering weak colonies over strong ones.
3/4 x 1 1/2" rim with 1/8 x 3/4" rabbets on both top and bottom to accept the two pieces of 1/8" galvanized hardwarecloth.