Measures 4 5/8" x 2 5/8" x 1/2". There are a few differences between the Jaw Jackers and traditional knuckles. First, they are made out of lightweight polymer and not metal. They also have projections on top and bottom to add two additional striking points, and lastly the space in the middle of the Jaw Jackers acts as kind of a leaf spring absorbing shock during frontal strikes. Very comfortable and lightweight.