Let the critters remove themselves with this system. SP45 is perfect for red and grey squirrels and similar sized rodents. It's extremely simple to use and very effective. SP45 consists of one E40 excluder and two SPT45 repeating traps (with two trap doors). Attach the E40 excluder over the animals den opening with the mounting wings. Slide one of the SPT45 repeating traps over the E40 and hook into place. As critters exit, the excluder will direct them into the repeating trap. SPT45 repeating traps have trap doors at each end to allow you to caputre animals both leaving and entering the den. To remove trapped animals, unhook the SPT45 repeating trap from the E40 and replace it with the other one included with this kit. This kit has a 4 x 4" opening and is designed to be tacked up over 4" wide or smaller openings.