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What are the parts of a protractor
and depth gauge?

Shop for Protractor Sets

Top: Protractor; middle: Locking nut; bottom: Rule/Blade; Starrett, protractor and depth gauge

Protractor

Blue, semi-circle, protractor, 180 degree The protractor resembles a normal 180 degree protractor. It can be used to set the angle of the rule.
A square protractor and depth gauge  Sometimes the protractor may be square in shape.

Rule or blade

Part of the rule/blade; protractor and depth gauge; Starrett The rule (or blade) is the part used to measure depths.

Locking nut

The locking nut; protractor and depth gauge, Starrett The locking nut secures the rule in place, meaning that the angle can be secured at any angle the user desires.