All steel construction. Each jack includes a 5" x 8" steel base plate and frame mounting plate. The crank turns easily due to a thrust ball bearing located at the junction of the drive screw and primary trunion. The entire jack is zinc plated and the handle is chromed. One model will fit most RVs regardless of the ground to frame clearance because it can extend from 4-3/4" to 24-3/16". Sold individually.For stabilizing and leveling purpose only. Never use for lifting, changing tires or supporting weight of any vehicles.