Description:Joinery Edge Principle: TTKJ t-square secret is a series of precision machined indexing and spring holes, A long-tolerance indexing pin that connects to them. The pin snaps into place, giving you confidence that it is accurate. Three sizes available: it is 10 inch, 15 inch or 20 inch. Both edges of the blade are laser engraved with an inch scale in steps of 1/32. 004" total cumulative error on blade length. The thin, satin stainless steel blade is easy to read and minimizes parallax error. Excellent wood stacking tools: Even if you're not working at an angle, this is a wood stacker that can reach almost any project. The blade has the same exclusive saw tooth Design dies found in our new precision stainless steel woodworking squares. There is a notch every sixteenth inch along the blade. Simply drop the pencil into the cutout and move your head along the edge of the magazine to create a perfectly parallel line. Material: Metal Color: Silver Size: 10 inch, 15 inch, 20 inch Measuring Range: 0-70 Degree Measuring Accuracy: 1mm Type: Angle RulerPackage Included1 * Carpenters Edge Principle