Makita B-66313 3‘1/8" x 24" SDS‘MAX Tunnel BitMakita B 66313 Makitas 3 1 8" x 24" SDS MAX Tunnel Bit is designed to drill larger holes in masonry for piping, ventilation, and electrical installations. This bit is ideal for drilling holes in concrete, block, and brick where the depth of the hole exceeds the depth of a standard core bit. The B 66313 features a solid tungsten carbide head, a carbide tipped centering point for more accurate drilling, and a solid one piece system that transfers power