Gauge blocks, also called gage blocks, are metal or ceramic blocks that have been ground and lapped to exact, specified lengths. They are used to calibrate precision measuring equipment such as micrometers and calipers, and as a dimensional standard in manufacturing, inspection, research and education. Each block is rectangular, with very flat, parallel measuring surfaces. Gauge blocks are usually supplied in sets with many varying lengths. Larger blocks can be constructed through the process of "wringing": sliding two blocks together, which causes the extremely flat surfaces to adhere to one another. Gauge blocks may also be referred to as Jo blocks, Johansson gauges, slip gauges, or Hoke blocks.