I use the GripMate clamps with my WorkMates a lot. Unfortunately Black and Decker stopped making them many years ago. If you pick up a used set of the GripMate clamps make sure they have the orange plastic collar, they are worthless with out it and it is often missing.
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I have several generations of workmates and there were some changes over the years. The older ones like pictured above used good plywood for the tops. The newer ones use particle board which is a definite downgrade. The locks on the legs went from metal to plastic but I haven't had any problems with the plastic leg locks.
For anyone that has an old workmate with broken plastic parts here is a great deal on plastic parts to freshen up an old bench:
Black and Decker: WM225 Type 1 Workmate, WM225 Type 2 Workmate, WM225 Type 5 Workmate, WM225 Type 6 Workmate, WM-225 Work Mate Models. Includes: (1) - Hardware Starter Bag With Swivel Pegs 242829-03. Replaces B&D part numbers: 242829-03, 24282903.
www.ebay.com