【6 Different Slot Diameters】: 6 pieces square hole drill bits with different slot diameter (1/4 inch, 5/16 inch, 3/8 inch, 1/2 inch, 9/16 inch. two pictures of My slot mortiser, based on a couple designs. . Jan 28, - My slot mortiser, based on a DIY And Crafts · Woodworking. Jun 24, - In this video I make a handheld cordless slot mortiser using the Makita trim router and some scraps of wood and metal from.