ATTENTION: This holder ONLY FITS FasTrak Flex transponders that are from 2020 OR NEWER that measure 4" x 1-5/8" x 3/8". Holder does not fit old versions with a vertical sliding switch. Please see the photos for reference. Installation is simple! Your FasTrak toll tag slides in and securely snaps into the holder. Two included suction cups attach the holder to your windshield so you no longer have to worry about adhesive residue on the glass. Easy to relocate to a different vehicle! Prior to installation, clean the area of your windshield where you intend to install the holder. There are (2) alcohol pads included with every holder. A glass cleaner like Windex is also perfect - ensure that there are no oils or streaks left, and glass is dry. Place the holder on the windshield, and firmly press down on the tips of the suction cups to squeeze out all of the air. NOTE: These mounts are 3D printed and have minor inconsistencies in the surface finish. These do not affect the integrity of the mount.