Our carpenters combination square set has a mitre square, center head, and protractor on a single 12" stainless steel blade marked with both imperial and metric measurements.
The square has a built-in spirit level viewable from all sides with a small scribe screwed into a storage spot in the head. The protractor head works between 0 and 180 degrees. Use the centering head to find the center of round work (ideal for turners). Thanks to knurled brass knobs all round, all 3 heads are removable and adjustable.