These compoents fit into the brake calipers and allow for the slider pins on the carrier to fit into the centre of the bush. The allow a small amount of lateral movement and reduces vibrations usually by 100% so long as it is lubricated. You must not use copper grease to lubricate these components. Only silicone grease or red castor rubber grease should be use to lubricate EPDM rubber components. Copper grease will attack EPDM rubber used on brake calipers.