Invented in the USA by Mr. Porter in 1891 The basic principle of its use is simplicity itself - a one way valve. Place the escapes in the crownboard slot/s with the top hole uppermost. Check that the springs are 3mm apart. This supplies just enough tension for the bees to pass through yet are close enough together to prevent their return. Remove the queen excluder and put the crownboard in its place below the super/s to be cleared. Bees leave the super, pass through the 22mm diameter hole and into the chamber of the escape. Once there the bees have two escape routes through the springs. If used properly, bees should clear supers over a 24 hour period. Overall size 40mm x 110mm.