Features: Accepts test indicators with dovetail clamping mechanism. Dial gauges can be held by the 3/8 or 8mm diameter stem or by the lug backing plate. Arm has 3 articulating joints that can be locked with the single hand knob. The rotary knob switches natural magnet on or off. The precision surfaces and the bottom V are securely fastened to the ferrous work piece or machine table when the rotary knob is in the on position.