An accessory unit for pneumatic position control is available to monitor that the Swing Clamp is in "clamped" position. This simple, reliable unit consists of a stainless steel housing with a spring-loaded control tappet. To operate the tappet, a control bracket must be attached to the rear of the clamping arm. This bracket must be adjusted so that it first contacts the tappet during the downward clamping stroke, after the full swing stroke, at a height where it will not bottom out on the housing at full clamping stroke. When the clamping arm reaches "clamped" position, the pressure control is closed and the pressure built up at the pneumatic port can be evaluated with a differential pressure switch. Parallel connection of up to three controls is possible with a single differential switch.