Loading... Please wait...Base Plate. Attach base plate to any flat surface via four mounting holes that are countersunk for drywall screws or flathead machine screws. Add Base Plate Blocks and you have a solid starting point to build off of. Base plates are 3/8 inch thick, drilled and tapped for 1/4-20 fasteners. This Base Plate is compatible with the 15 mm, 375, 500 and 750 series Base Plate Blocks.