This solid brass slot can be installed in a door or on a mailbox. The attached mounting bolts on the back are 3/4 inch long and have their original washers and nuts. The width of the door or mailbox can not be over 1/2 inch in order to allow for threading on the nut. The bolts are 6 3/4 inches apart. The mail slot measures 8 inches by 2 7/8 inches. The opening for the mail is 5 1/4 inches by 1 1/2 inches. The swing door hangs freely and closes on its own weight.