Starrett combination square consist of a machine-divided, hardened and tempered steel rule (or blade) on which is mounted an adjustable square head. A reversible lock bolt allows the blade to be turned over or end-for-end without removing the lock bolt or nut. This ensures true alignment of the blade and heads. Square head are made of cast iron and are not to be confused with the cheap imitation plastic or die cast heads on the market. The value of Starrett tools is that they are accurate and will last. As the name indicates, this tool can be used for many different purposes - a complete substitute for a whole set of common solid try squares, a 45 degree metre, a depth gauge, a height gauge, a marking or scribing gauge, a level, a plumb and, by withdrawing the blade, it can also be used as a precision rule. This saves littering the workbench with too many tools, each being necessary but may be used less. This results in the goal of all good craftsmen - better accuracy and greater efficiency.