This square is not a standard production model but one made to a special design. Available with a 100mm (4") blade or a 150mm (6") blade, it features a slimmer than normal stock and an accuracy guaranteed to be better than 0.001" per inch, exceeding our regular machinist's squares. It doubles as a try square and a precision square, suitable for both layout work and machinery set-up and checking. The precision openwork casting not only provides the accuracy required but avoids the stock-heavy feel of most machinist's squares. The blade locks securely in any position from full left to full right. Made in USA.