Lab cables are frequently used to connect electrical power supplies to circuit boards, devices under test and laboratory equipment, such as stepper motors, centrifuges, analysers and bespoke assemblies. For low voltage circuitry, cables with a diameter of 1 millimetre may suffice, though 4mm diameter cables are more commonly used for most laboratory electrical connections. Thicker lab cables with diameters up to 6 millimetres are suitable for applications that draw high current. It is important to use the appropriate thickness of cable to avoid the safety risks caused by overheating. Multi-Contact and other leading manufacturers produce a wide choice of Cat I, Cat II and Cat III unshielded twisted pair cables that comply with RoHS material safety standards; full details and cable dimensions are included in product data sheets. Cable plugs are often connectable in stacks for the straightforward connection of parallel circuits, while safety plugs are an extra precaution when working with live electrical systems. Cables with safety plugs feature sliding insulator sleeves to protect against accidental skin contact with the live metal conductor; other features include tough contact springs and shatterproof grips. Finally, laboratory test leads with probes are used for checking and monitoring circuit input and output performance with digital multimeters, oscilloscopes and other measuring equipment.