T-Square Cap for Ruler

A cap that turns a ruler into a t-square.

Designed for use with ProArt stainless steel rulers (specifically 7720-18 and 7720-24) but should work if the ruler is 33.5mm or 1 5/16" wide.

20mm of the measured surface of the ProArt rulers sits in the cap, so add 20mm or 13/16" if you're using this to measure.