Throughbores

A throughbore, or through bore, is a hole that extends completely through a part from one face to the opposite face. Throughbores are typically produced by drilling, boring, reaming, or honing and are specified for a precise diameter, straightness, and surface finish. They are used to accommodate shafts, pins, fasteners, or services such as fluids or wiring, and to provide alignment or pass-through access. The term contrasts with a blind bore, which does not reach the far surface.

Applications are common in mechanical components such as engine blocks, hubs, housings, flanges, gears, and manifolds. A throughbore can serve as a bearing surface, a passage for lubricants or coolants, or a mounting or alignment feature that permits a fastener or sleeve to pass completely through the part.

Design and manufacturing considerations include maintaining straightness and concentricity with adjoining features, controlling diameter along the full length, and achieving the required surface finish. Tolerances govern mating fits with shafts or sleeves; clearance fits enable sliding assemblies, while interference fits require appropriate press or shrink fits. Thermal effects and assembly misalignment may influence the selected bore size and finish.

Inspection typically uses bore gauges, pin gauges, dial indicators, or coordinate measuring machines to verify diameter, roundness, and straightness, as well as surface roughness. Deburring is often performed to remove sharp edges that could initiate cracks. The throughbore concept is widely used across industries to enable assemblies and service passage through components.