Some 2 post, mobile column and 4 and 6 post lifts use a mechanically driven screws to raise and lower the arms and platforms. Running on the screws are a nut. These are made from a softer material than the screw and the nuts are designed to wear as a less costly item than the main screw. They are commonly made from phosphorus bronze or a modern plastic. They have wear markers to show when they are due for replacement.