The Universal Frame Grip design can be used on BOTH Plastic and Wood Bee Frame Foundations from all standard Suppliers and Manufacturers sold today. Locking Feature – This is accomplished by simply turning clockwise a clamping knob attached through a special sliding locking arm. The Mule-Grip™ unit adjusts to the width of the frame. It will stay locked even when set aside until the clamping knob is turned counter-clockwise to release its hold. Reduces worry of dropping bee frames and damaging comb, killing bees especially the queen.