# Through-holes

Holes that pass through the intended material: function, extent, breakthrough, edge condition and inspection.

Reviewed: 2026-11-01

Tags: parts-and-design, holes, drilling, machining

## Extent is separate from function

A through-hole opens through the material. Specify its diameter, location and finish separately.

In the ideal 6.0 mm drill and 118° point example, the tip extends **1.803 mm** ahead of the full-diameter plane. The tip must travel beyond **11.803 mm** from first contact to clear that plane through a 10.0 mm plate. First visible breakthrough alone does not demonstrate full diameter. Actual tooling and safe exit clearance govern the machining depth.

A drawing should identify which walls or bodies are penetrated. A hole through one wall of a hollow component is not necessarily a hole through both walls, and a cross-hole may intersect an internal passage before reaching the opposite exterior. Use a section or explicit end reference when a simple “through” label leaves the material extent ambiguous.

## CAD end conditions and design intent

**SOLIDWORKS 2025 Help** defines **Through All** as extending a feature from its sketch plane through all existing geometry, while **Through All—Both** extends in two directions. **Blind**, **Up to Next** and **Up to Surface** have different termination rules. Those are software definitions, not interchangeable drawing instructions. [SOLIDWORKS 2025 end conditions](https://help.solidworks.com/2025/English/SolidWorks/sldworks/c_End_Condition_Types.htm)

Select the end condition that represents the intended part, then recheck it when the model changes. A through-all feature can cut more material after a design change than a fixed-depth feature; a fixed-depth cut can stop short after a thickness increase. Inspect the resulting geometry rather than relying on the feature's name.

SOLIDWORKS **2026 Hole Series** can create holes through intersecting assembly components and specifies an end component; its documentation notes that the individual parts contain externally referenced features. An assembly-level hole definition therefore needs review in the released component models as well. [SOLIDWORKS 2026 Hole Series](https://help.solidworks.com/2026/english/SolidWorks/sldworks/c_Hole_Series_Overview.htm)

## Define the acceptance characteristics

| Field | Information to make explicit |
|---|---|
| Size | Diameter or other opening profile, limits and units. |
| Location | Datums, axis orientation and pattern relationships. |
| Extent | Intended walls/components and any intersecting passages. |
| Surface | Functional bore finish and applicable inspection stage. |
| Edges | Entry/exit chamfers, burr requirements and permitted breakout. |

“Drill through” does not establish a close-fitting bore. Where size or form needs finishing, identify the finished requirement separately from the preceding drilled hole. Likewise, threading a through-hole requires its own thread designation and usable engagement definition; through extent does not prove that every axial portion contains a complete thread.

For fasteners, identify the appropriate clearance series rather than using nominal thread diameter as hole diameter. **ISO 273:1979**, edition 1, June 1979, tabulates general-purpose clearance holes in fine, medium and coarse series; its public record lists a corrected English version July 1992 and confirmation in 2024. It expressly leaves special applications to design requirements. This scope is a fastener-clearance reference, not a position tolerance or load rating. [ISO 273 publisher record](https://www.iso.org/standard/4183.html)

## Drilling reach and exit conditions

Protolabs' machining guidance notes that part size, hole diameter and material can prevent a cutter reaching through, even when the geometry is open. It says machining from both sides is possible in some cases, subject to design analysis. These are service-specific capabilities; do not interpret “through” as a guarantee of single-setup access. No technical revision date was verified on the live page. [Protolabs complex machined features](https://www.protolabs.com/resources/design-tips/mastering-complex-features-on-machined-parts/)

Review the actual tool, holder, workholding and space beyond the exit. If machining from opposite ends, agree the resulting alignment, transition and inspection requirements. Merely connecting two drilled openings does not establish a continuously accurate bore.

Sandvik Coromant's irregular-surface guidance identifies uneven cutting-edge forces and intermittent contact at inclined entries/exits. It also discusses chip evacuation and difficult deburring at crossed holes. The guidance is divided by drill type, so its numerical settings should not be exported as one universal breakthrough recipe. No issue date was verified on the cited page. [Sandvik Coromant irregular-surface drilling](https://www.sandvik.coromant.com/en-gb/knowledge/drilling/irregular-surface-drilling)

A sloping or curved exit can therefore need a different process review from a perpendicular flat plate. Locate critical intersecting passages and assess their internal edge condition, not only the two visible exterior openings.

## Original drill-point geometry example

**Illustrative assumptions:** a 6.0 mm drill has an ideal symmetric conical point with an included angle of 118°, and it enters perpendicular to an ideal flat plate. Ignore cutting-edge details, wear and clearance margins.

The point length from tip to the plane of full diameter is

`h = (D/2) / tan(118°/2) = 3.0 / tan(59°) ≈ 1.803 mm`.

For an assumed **10.0 mm plate**, tip travel from first contact must therefore exceed approximately **11.803 mm** for the ideal full-diameter plane to pass the back surface. This is geometry, not a commanded machining depth: actual tooling, thickness variation, setup references, deflection and safe exit clearance require additional review.

The example explains why the first visible tip breakthrough is not evidence that the full cylindrical opening has cleared the exit face. It also does not apply unchanged to flat-bottom tools or other point geometries.

## Edges, cleaning and functional inspection

Specify burr removal and chamfers where they affect handling, mating surfaces, sealing or passage cleanliness. An unspecified “deburr” instruction should not be assumed to create a controlled countersink diameter or angle. Conversely, an added edge break must not remove a functional seating surface or reduce required engagement without review.

Gühring lists tools for front/back chamfering and removal of burrs at crossed holes, illustrating that exit and internal intersections may need deliberate operations. Tool availability does not itself establish that a particular buried edge is accessible or meets the required acceptance. No issue date was verified on the webpage. [Gühring countersinking and deburring tools](https://guehring.com/uk/products/countersinking-and-deburring-tools/)

Inspect the actual required characteristics: a visible opening establishes neither diameter throughout the bore nor positional accuracy. Where the hole conveys fluid, permits a pin to pass or receives a fastener, qualify that function with the appropriate dimensional and assembly requirements. A simple trial insertion is not a replacement for every specified characteristic.

## Release checklist

1. Define hole function, dimensions, datums and intended through extent.
2. Review cutting access, reach, intersections and exit geometry.
3. Specify required finishing, edges and cleanliness.
4. Verify size, location and usable extent at the agreed inspection stage.
5. Preserve the released model/drawing and actual process requirements together.

For agent-readable records, store through extent independently of clearance class, thread specification, finishing process and performance acceptance. Retain source version, units and measurement references; distinguish a CAD end condition from a manufacturing instruction.