Fuller Hollow Mortising Chisels are for making square mortises in one stroke and oblong mortises with each succeeding stroke. The Hollow Mortising Chisel requires a matching Mortising Chisel Bit.
These mortise chisels do a fine job just like all the other Fuller cutting tools. They work best in a dedicated mortising machine. And don't forget to buy the matching drill if you don't already have one. A pleasure to use.