What Is a Sine Bar?

A sine bar is a hardened steel bar set on two cylinders whose centers are an exact distance apart. They are used by machinists in setting materials at precise angles during milling, grinding and inspection.

A sine bar is often used with gauge blocks. The sine bar forms the hypotenuse of a right triangle, while the gauge blocks form the opposite side. The height of the gauge blocks is found by multiplying the sine of the desired angle by the length of the sine bar. To find the height for a 13-degree angle, multiply the sine of 13 by five. The result of 1.124 would then be measured using gauge blocks of appropriate thickness.