5/16” Mortising Bit for Hollow Chisel Mortising Machines — 9-1/2” Long

The HMC313B is a 5/16-inch mortising bit for hollow chisel mortising machines, supplied in the 9-1/2-inch long length. In hollow chisel mortising, the drill bit and hollow chisel work together: the bit bores the round bulk of material while the hollow square chisel, which surrounds the bit, is simultaneously pressed in to produce clean square corners and flat cheeks. The 5/16-inch size sits between the 1/4-inch and 3/8-inch mortise widths, matching 5/16-inch tenons and loose tenon stock where a 1/4-inch joint is too light and a 3/8-inch joint removes too much material from the stile. The 9-1/2-inch length suits deeper mortises and machines with greater spindle travel. This bit is for use inside the matching HMC313C hollow chisel; order HMC313S for the complete chisel and bit set. Confirm machine compatibility (chuck size, collet, and spindle travel) before ordering — mortising bits require the correct bit-to-chisel clearance for clean operation.