In use, the blocks are removed from the set, cleaned of their protective coating (petroleum jelly or oil) and "wrung together" to form a stack of the required dimension. Gauge blocks are calibrated to be accurate at and should be kept at this temperature when taking measurements. This mitigates the effects of thermal expansion. The wear blocks, made of a harder substance like tungsten carbide, are included at each end of the stack, whenever possible, to protect the gauge blocks from being damaged in use.