We have hunted high and low for the best drill bit and counterbore combination for timber frame assembly. These are ideal for countersinking GRK Fasteners in floor joists and roof rafters for a clean assembly.
The drill bit is made by ITW and is cost effective and can be replaced. The counterbore is made in the US by W.L. Fuller Company and the high speed steel is durable and can be sharpened. It will last you many frames.
Drill Bit: 1/4-in x 12-inches long with a 9-in flute. High Speed Steel and an all-purpose point.
Counterbore: Type 'X' 3/4-in cutting diameter, 1-in overall length -- 'designed to cut faster and deeper in hardwoods. It is adaptable to high or low speed spindles and hardened for long service. The four-blade rugged construction cuts a smooth hole and stays sharp longer.