Cable-entry geometry inspection starts with the functional surfaces and the drawing’s datum system. Before choosing a measuring instrument, we need to identify the opening, its axis, the seating face and the actual seal footprint. A coordinate measuring machine can establish relationships between sampled features; a thread gauge, surface instrument or local dimensional tool answers a different question.
The useful result is a report that says which feature was measured, in what condition, against which requirement. A precise bore diameter alone leaves the seal land, wall remaining below a recess and position relative to nearby hardware unresolved. This guide turns those different features into an inspection method you can explain and repeat.
Start with the drawing’s functional references
A datum is the reference used to establish the orientation or location of specified features. The drawing identifies the datum features and their order. The part setup must follow that system, because a convenient clamping face is not automatically the intended reference.
For a gland plate, the enclosure mounting face might be a datum feature, with edges or holes establishing the remaining directions. The entry axis may then have a specified position or orientation relative to those references. That is one possible arrangement; I would obtain clarification if the drawing leaves it undefined rather than silently inventing a datum scheme.
ISO 1101:2017 defines the language and interpretation of geometrical specifications. It does not supply a universal flatness or position tolerance for a cable entry. Copy the actual requirement, feature identifier and drawing revision into the measurement plan. Keep size, form, orientation and location as distinct characteristics when the drawing controls them separately.
For example, a hole can have an acceptable diameter while its axis is misplaced. A seating face can be correctly located but locally damaged. Each function needs inspection of the feature that matters to it; one successful measurement cannot stand in for the complete interface.
Read the recess as well as the through-hole
A counterbore is a cylindrical enlargement with a flat shoulder or floor. Its diameter and depth define space around the smaller opening. A countersink is a conical enlargement; its angle and size describe an angled mouth. A spot-face creates a local flat seating area, often on an otherwise uneven surface. A seal land is the surface actually contacted by the specified seal, whether that surface was produced by spot-facing or another process.
These names describe different things. “Spot-face” identifies a prepared feature; “seal land” identifies a functional contact area. Mark the seal’s inner and outer footprint on the drawing so you can see whether the prepared flat area covers it continuously.
The sections are schematic, with no dimensions or standard seal proportions. The selected gland and enclosure drawings determine the required geometry. A deep counterbore removes material that could otherwise support a locknut or threaded engagement. A countersink can reduce the flat annular area available to a face seal. Those are reasons to measure both the opening and its surroundings.
The smallest remaining material thickness at the recess matters here, rather than the original stock thickness. Where the recess approaches a folded edge, boss or adjacent hole, the local geometry matters. The entry-hole selection guide addresses mounting and clearance; the inspection plan needs the finished limits for the particular feature you selected.
Match the measurement method to the feature
A CMM measures point locations and evaluates features from those data. Its usefulness here is the relationship between surfaces, axes and datums. I would use it when several entry positions or orientations must be related to a common reference, then select additional methods for characteristics it does not adequately capture.
| Characteristic | A suitable method to consider | What I would record |
|---|---|---|
| Plain-bore size | Bore gauge, suitable internal measurement or CMM strategy | Size requirement, sampled depths and directions |
| Entry position and orientation | CMM or another validated coordinate method | Datum alignment, fitted feature and evaluation method |
| Counterbore diameter and depth | Internal measurement, depth measurement or CMM | Recess floor reference and remaining wall requirement |
| Countersink geometry | Appropriate angle/profile method or CMM | Controlled angle, size and accessible sampled surface |
| Thread acceptance | Specified thread plug or ring gauges and procedure | Thread standard, gauge identity and applicable acceptance result |
| Seal-land texture | Surface-texture instrument and prescribed evaluation | Parameter, direction, settings and measurement location |
| Burrs, scratches and coating damage | Defined visual inspection, with suitable magnification if needed | Location and the drawing or workmanship criterion |
These are method choices, not automatic approvals for every tolerance. A caliper may be useful for identification yet inadequate for the acceptance limit. A few CMM points do not reproduce a surface-texture trace. A thread gauge addresses its specified thread acceptance task; it does not measure the seal land’s flatness.
ISO 10360-2:2009 concerns acceptance and reverification of CMM performance for linear dimensions. Its stated scope is Cartesian CMMs with contacting probes in discrete-point mode, and it does not explicitly cover optical or non-Cartesian machines. Machine verification remains separate from validating the strategy for this particular part.
Make the setup explain the result
The measurement plan should describe the fixture, alignment and probing approach clearly enough that another operator can reproduce them. Support a thin plate without pulling it into a flatter shape than its specified inspection condition. Otherwise, the report may describe the clamped shape rather than the required part condition.
Choose the probe and access direction for the recess being inspected. Identify the points or scan paths, their distribution, the fitted geometry and any filtering. A sparse sample can miss a local defect; more points in the same easy-to-reach patch do not necessarily represent the rest of the surface. Use the drawing’s evaluation rules and a validated sampling strategy.
The NPL guide on CMM measurement strategies addresses sampling, alignment, cleanliness, temperature and surface effects. For our inspection plan, that framework prompts practical questions: Did the probe reach the intended floor? Did a burr enter the fit? Was the part stable in the fixture? Does the software output correspond to the drawing characteristic?
Measurement uncertainty also belongs with the result. NIST’s metrological-traceability policy distinguishes a traceable measurement from one that is necessarily fit for its intended use. A calibration certificate supports the measurement chain; it does not, by itself, settle a close conformity decision. I would use the agreed decision rule and the applicable uncertainty rather than round a borderline value into acceptance.
Inspect the part in its specified finish condition
Machined, plated, painted and assembled conditions are different inspection states. Identify the state to which each drawing limit applies. A dimension taken before coating cannot automatically stand in for a finished dimension, and a coating can change both available clearance and the surface under a gasket.
For a finished gland plate, examine the bore edge and the full seating perimeter after the specified finishing and cleaning operations. Look for local buildup, masking boundaries, burrs and damage where the seal or retaining part will actually sit. If the drawing calls for a prepared electrical contact area, keep that area distinct from the sealing surface and follow the specified corrosion-protection treatment.
A useful record might read: “Counterbore depth measured from datum A on the finished coated part, using the approved setup and drawing revision.” That makes the reported number interpretable. “Depth checked” leaves the reference, condition and requirement unclear.
Connect geometry acceptance to assembly checks
Once the geometry is accepted, the gland still needs its permitted cable, seals, accessories and installation method. IEC 62444:2010 addresses construction and performance requirements for complete cable glands within its scope. A coordinate report for a panel opening is evidence about a different object and characteristic.
Keep the dimensional report alongside the relevant installation and functional evidence. The dimension report can establish the inspected interface geometry. Assembly inspection can establish that the specified parts and installation conditions were used. Applicable sealing, retention or electrical tests then address their own performance requirements. Clear separation makes it easier to investigate a failed joint without discarding useful measurement evidence.
Conclusion
The datum system and the surfaces that support, locate and seal the assembly give a cable-entry inspection its starting point. The opening diameter is one characteristic among several. Recess geometry, remaining wall and the seal footprint can each change how the gland seats, even when the nominal entry size is correct.
Build the measurement method around those features, then record the setup, finished condition and conformity basis. That gives you a repeatable dimensional result and a clear handoff to assembly and functional verification. A good inspection report makes the limits of each measurement visible without losing the engineering information it provides.
FAQ
Is a spot-face the same as a counterbore?
Both can create a flat surface around a hole, but their drawing purposes differ. A counterbore is a cylindrical recess with controlled diameter and depth. A spot-face prepares a local seating surface. I use the actual callout and limits rather than inferring depth or function from a similar-looking section.
Can a CMM replace the thread plug gauge?
A CMM can measure selected thread characteristics with an appropriate method. That does not automatically replace the specified thread-gauge acceptance procedure. I retain the required gauging method unless the controlling specification accepts an alternative and that alternative has been validated for the task.
Does a flat seal land prove that the entry is waterproof?
No. A flatness result describes the evaluated surface. Sealing also depends on the correct seal, footprint, finish, compression, cable and assembled interfaces. I treat geometric acceptance as one input to the complete assembly’s applicable ingress-protection evidence.
Should the plate be measured before or after coating?
Use the condition specified for each drawing requirement. Process measurements before coating can help control machining, while finished-part limits require evidence for the finished condition. I label both states explicitly so a pre-coating result is not mistaken for final acceptance.
Sources and technical references
- ISO 1101:2017 — Geometrical tolerancing (EVS), accessed 2026-10-23.
- ISO 10360-2:2009 — Acceptance and reverification tests for CMMs measuring linear dimensions (EVS), accessed 2026-10-23.
- NPL — CMM measurement strategies, Good Practice Guide 41, accessed 2026-10-22.
- NIST — Metrological Traceability: Frequently Asked Questions and NIST Policy, accessed 2026-10-22.
- IEC 62444:2010 — Cable glands for electrical installations, accessed 2026-10-22.