This shelf uses the GRS BenchMate fixed mounting plate to hold your engraving block below the front of your bench. Jewelers especially like this because the top of their block is the same height as their bench pin. The Standard Shelf, used mainly with the Standard Block and Magnablock, has some up and down adjustability. The Large Shelf has more height adjustment and a larger tray, especially for the Positioning Vise (#003-541). The Large Block Shelf includes the Adjustable Height Bracket (#004-666) without the Fixed Mounting Plate (#004-557). Here, the Adjustable Height Bracket is attached directly to the Large Block Shelf without the Fixed Mounting Plate, giving additional weight support and stability for holding larger vises. The Fixed Mounting Plate is not required.