Most newer cars have specific areas in the chassis designed for safely lifting the vehicle. These jack points require a pinned adapter that professional technicians use with their hydraulic car lifts. This jack pad locks into the the car by simply turning the unit and is specifically designed to be used with most floor style hydraulic jacks. It's low profile design gives your jack sufficient clearance to slide under the car and then safely lifts it to minimize potential slippage. Come's with a rubber top pad to eliminate the undercoating of your car from being damaged. If you are using these pads with a car lift, you will need (4) units to properly lift the vehicle. All steel construction, water jet and tig welded seams with a powder coated red finish that will last for ever. The OD of these is 3.52" and the ID is 3.15".