Pete, the spring has a plastic ribbed cover fitted to the bottom coil which isolates it from the cup on the damper, the top has a Metalastic rubber cup where one side sits in the spring, and the other cups the strut top mounting.
What is most important is when decompressing the spring that the top rubber cup is allowed to seat squarely into the bearing, failure to do this will result in the oil seal of the top bearing becoming damaged resulting in early failure
The ZT is easier to fit springs to than the 75, as the free length of the spring is shorter, which also means easier to fit the assembled strut to the car
Brian
