SOLD 21 mm special Strut Socket is needed if you install springs or struts, as you have to crank the socket and keep an allen key in place at the same time. You can buy the expensive OEM socket or get a 21 mm deep socket and cut it to match - which is what i did here. I don't have the car anymore so why cut one yourself when you can get this one for price of socket plus shipping. Shipped to 48 contiguous states for $10.