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.