Class 3(Class III) forklift forks are designed to fit on an ITA class 3 carriage and by definition that would encompass forklifts from 5500 lb basic capacity to less than 10,000 lbs capacity (24" load center). Specifically what makes them unique is the mounting distance between the hooks (hangers) and the draft angle on the hooks.
It is possible to have a class 3 carriage on other sizes of forklifts, generally to accommodate an attachment, where the net capacity of the combined unit will fit within the standard class 3 parameters.
Class 3 forks come in many styles/confogurationsd such as pallet forks, fully tapered and polished forks, lumber forks, plywood forks, coil forks, block forks, and virtually any specialty known.