The EZ-Read finish also increases friction to better secure your square against your lumber when using it as a saw guide. The Johnny Square is highly durable and accurate. Its solid aluminum body construction with CNC machined edges ensure an accurate reading every time. This rafter square also features continuous scribing notches that are ideal for ripping at 3-1/2" and 5-1/2" as well as handy markers that measure 2x4 board dimensions of 1-1/2", 3" and 3-1/2".