These jack blocks are used between steel jacks and the steel car bodies and axles, to stop steel on steel contact. They get heavy use. The black handles have chain inside them. The end handles on the 6″ x 8″ Maple Blocks are so they can be manoeuvred underneath a rail car bogie. These look like furniture now, but they will be greasy and dirty and beat up in no time. We make any size custom blocking.