When the surrounding fixture leaves no room for a jaw to slide clear. An angular jaw folds back out of the working envelope, so a part sitting in a nest, a pallet pocket or a chuck can be reached from above without the gripper body having to lift as far. The trade is holding accuracy: a swinging jaw meets the part on a tangent, so it locates less precisely than a flat parallel face.

Because the cam or lever ratio changes through the swing. Force is highest where the mechanism has most advantage - usually near the closed position - and falls away as the jaws open. A catalogue figure taken near closure will not be available at mid-arc, so the part has to be gripped near the angle the rating assumes.

The arc swept by the longest point on the finger, plus the finger's own thickness, measured in the plane of the swing. This is larger than most layouts allow for, and the usual mistake is checking clearance in the closed position only. A quick check is to draw the fully open finger tip against the nest wall before the fingers are made.

Single-acting versions use a spring to drive the jaws one way and air the other, which halves the plumbing and gives a defined state with no air. Spring-closed units keep hold of the part on air loss; spring-opened units release it. Double-acting versions give more force in both directions and are the norm where cycle rate matters.

The cam track and its follower, and the jaw pivot bushes. Wear shows as a growing angular backlash - the jaw can be rocked by hand with air applied - and as a jaw that no longer closes square onto its partner. Because the mechanism is enclosed, the check is a hand test at service rather than an inspection.

Within a narrow band. The jaws only touch the part squarely at one angle, so a diameter change moves the contact onto the edge of the pad. Where the size range is wide, either shape the finger pads to a compromise arc or move to a parallel gripper, which keeps flat contact throughout the stroke.

Through tapped holes and dowel locations on the body face or side, chosen so the swing plane matches the approach direction. Getting the swing plane wrong is a common layout error, because the gripper will still bolt on and still cycle - it simply sweeps into the fixture instead of away from it.