Guardhouse Display Boxes#: ALUM-20. Size: 12x3.25x4 Color: Metal. Sold Individually. This multi-coin slab aluminum box holds twenty certified coins from any of the major grading services. Built with sturdy materials, this sleek aluminum box is crafted with attractive exterior fittings and has foam inserts for easier handling of the 20 certified coins. Guardhouse' aluminum slab boxes are perfect to keep certified coins safe when travelling.