strut joint assemblies which include built - in off - loading capability or mirror support systems allow a user to minimize the friction developed at the ball joint interface . each strut joint assembly includes an upper ball joint and a lower ball joint . each of the ball joints is sealed such that an internal compartment is created which can act essentially as an air spring . by raising the air pressure within these compartments , the load on the ball joint is reduced until the joint separates and air pressure alone carries the entire load . by adjusting the pressure to a value just below the separation pressure , the ball can still maintain contact with the ball socket and carry very little of the actual load . at this pressure , the frictional moment that can be generated by the joint is minimized and is , thus , greatly reduced from the frictional moment developed by a joint which is carrying the full gravity load of the mirror . the entire strut assembly may be translated using an adjusting screw at the lower end of the strut . once adjustment of the mirror position is complete , the joint may be locked by injecting an epoxy adhesive into the cavity between the strut shank shoulder and the potting cup of the mount pad and allowed to cure . after the epoxy is cured , air pressure may be released .