This is a slingshot front door suitable for square tubes, which requires the installation of square metal tubes or wooden boards. This front door is a dual-purpose front door that can be equipped with round tube rubber bands or flat rubber bands. The package contains screws required for installation, please securely fix them. Package list: slingshot front door, slingshot trigger, round rubber band, flat rubber band, screws. Rubber bands are consumables, please place them in a dark environment and prevent scratches to extend their service life. Please make sure to firmly fix each component to prevent it from falling off and causing injury.