The jaws of parallel-action pliers remain parallel regardless of the range of motion the pliers themselves are put through. Their jaws hold the object securely, even under very firm pressure.
• Choose parallel-action pliers when you need to hold a workpiece or other object securely while at the same time applying firm pressure to it.
• Choose parallel-action pliers when manipulating wire; you can feed the wire down through the throat and hold it firmly over the entire length of the jaw.
Parallel-action jaws stay secure regardless of pressure or force exerted on the handles or the placement of the workpiece within the jaws.
Applying pressure to regular plier handles exerts oblique, uneven pressure on the object being held and can cause the object to slip forward.