Door and board carry clamps are designed for heavy-duty lifting of sheet materials, like stone or marble. There are two basic designs, ones with a single handle and ones with two handles.
Door and board carry clamps are usually sold in pairs, as they are designed for lifting sheets which would be too heavy for an individual to lift. They clamp onto the edge of a sheet of material, either end, and can be used by two or more people.
The clamping pads of these carriers are either two large, flat surface pads, or four round gripping arms, two on each side. These are usually rubber coated to increase friction, so they grip effectively while protecting the surface of the material. Both types grip the sheet edge in the same way, but the flat pads have a larger surface area, spreading the load to avoid damaging the surface of the material being carried.
For even heavier sheets, or for extra grip, there are vice grip carry clamps. These use screw vice clamps to secure the carrier more permanently in place, rather than just being held by lifting the handles.