Joiner Square
Joiner's square - a measuring device used in carpentry . It consists of two boards fastened together at an angle of 90 °, which are usually metal (sometimes there may be squares with two different boards - wooden and metal). Usually there is a small notch in the inner corner. This prevents the accumulation of small particles at the junction and affects the evenness of the angles. Unlike a corner , its boards are wider. Joiner's squares have an error in measurement [ what? ] not more than 0.00051 cm. There are squares where the boards are attached at an angle of more than 90 ° - usually 120, 135 or 150 °.