throughopening

A throughopening is an opening or hole that extends completely through a part from one surface to the opposite surface. It is often called a through hole and is used to pass fasteners, pins, shafts, fluids, wires, or alignment features through a component. It differs from a blind opening, which terminates before reaching the far surface.

Shape and size of throughopenings can vary. The most common form is a circular throughhole produced by drilling and finished by reaming or boring to the required diameter and surface finish. Throughopenings can also be noncylindrical, such as rounded rectangles or slots, created by milling, EDM, or other processes to accommodate specific geometries or assembly needs.

Manufacturing approaches include drilling, punching, laser, waterjet, or additive manufacturing. Finishing steps may include deburring, honing, or deburring depending on the application and required surface quality. In mechanical drawings, the through nature of the feature is typically indicated by a hole that continues through the entire part, and depth is implied to equal the material thickness unless otherwise specified.

Dimensioning and tolerancing often focus on the nominal diameter, positional tolerances if alignment is critical, and any required surface finish. For throughholes used for fasteners or pins, clearance or interference fits may be specified. In electronics, the term “through-hole” is also used to denote holes through a printed circuit board for component leads, as distinct from surface-mounted features.

Applications of throughopenings include fastening, alignment, fluid passage, and electrical or mechanical interconnections within assemblies and structures.