This is an adapter designed to fit on select stone cutting blades which have pre-drilled 4 hole pattern near their center arbor. The adapter is made from durable lightweight aluminum and uses 4 #2 Philips screws to secure the blade. The adapter is designed to fit on all standard sized 5/8” 11T angle grinder shanks. This allows you to cut in tighter places compared to the standard 2 piece attachments.