throughbore

A throughbore is a cylindrical hole that passes completely through a component or assembly, providing an open channel from one face to the opposite face. It is contrasted with a blind hole, which stops short of the opposite surface. Throughbores are common in mechanical parts, housings, fittings and pipework, and serve functions such as accommodating shafts, fasteners, fluid or gas passage, wiring, or alignment features.

Design considerations for a throughbore include diameter, length, concentricity, surface finish, tolerances and any required transitions such as counterbores or countersinks. These factors affect mechanical strength, fit (clearance, interference or transition), wear characteristics and sealing performance. In applications supporting rotating elements or bearings, precise bore geometry and surface finish are critical for load distribution and life.

Manufacturing methods for throughbores include drilling, reaming, boring, broaching and electrical discharge machining (EDM), often followed by finishing operations to meet tolerance and surface requirements. Machining strategy must address chip evacuation and coolant flow to avoid tool damage and workpiece defects. Inspection commonly uses calipers, telescoping gauges, bore gauges and coordinate-measuring machines (CMMs) to verify dimensions and alignment.

Related terms include blind hole, counterbore, countersink and stepped bore. In electromechanical components, "through-bore" can also describe motors, encoders or bearings that feature a central aperture to allow passage of cables, shafts or tooling.