The EFS adapters is the hardware that ensures a safe and secure fit on the universal spare wheel. Every vehicle wheel has a specific PCD size for the lug pattern on their wheel. The adapters are placed inside each lug hole prior to installation. The combination of the installed adapter and black rubber O ring ensures a safe and secure fit once the wheel is tightened to the wheel hub. The adapters can be purchased by the set for any of our 4 or 5 lug wheels.