I have a mechanism where two parts are screwed and unscrewed and I wish to incorporate a system by which the number of screwing and unscrewing can be indicated. I have thought of a method using the erosion of material. As part of that, I have two components which will have a "soft material" between them. So with each screwing and unscrewing cycle a certain amount of material is eroded. And once the the total amount of material has been removed, the user will know that the manufacturer guaranteed life is over. Can I get any suggestion for commonly available soft materials?