Troyer Tunnels With Collar

Step 1).  You need to enlarge the hole on the front of door of each compartment of your T-14 house to a 3" round hole using a hole saw

Step 2). When enlarging this hole you need to make sure that the hole in the door is ¼" to ½" ABOVE the compartment of the house.  The compartment being where the martins are.  (If you do not do this step, when you insert your nest trays, they will block the entrance and the martins wont be able to get in.)

Step 3). Screw the tunnel with collar on to the front of the house aligning the opening of the collar around the hole you drilled.