Rectangular and square gauge blocks are used individually or connected together to produce precision lengths. Gauge blocks, also known as slip gauges, are rectangular (also known as Jo blocks) or square blocks (also known as Hoke blocks) of metal or ceramic with two opposing faces that are ground precisely flat and parallel at an exact distance apart. Square blocks have a hole so they can be used in conjunction with a rod for vertical positioning. Gauge blocks commonly come in sets with a range of standard lengths. Gauge blocks are commonly used in machine shops and in quality assurance and calibration environments.