Cable Gland Size Chart (Metric, PG & NPT)

Choosing a cable gland by its thread type alone is one of the most common causes of installation problems. Metric, PG, and NPT threads are not interchangeable, and even within the same thread family, the correct size depends on the actual outer diameter of the cable — not the panel cut-out or the enclosure's nominal opening size. Fitting the wrong size gland can loosen the cable's grip, break the seal, and drop the enclosure's IP protection rating.

This guide brings together the clamping ranges for Metric, PG, and NPT cable glands, explains how the three thread standards differ, and walks through how to read a cable gland size chart correctly before ordering.

Why Cable Gland Size Matters

Every cable gland is built around a clamping range — a minimum and maximum outer cable diameter it can seal and grip reliably. If the cable sits below the minimum, the seal cannot close fully and water or dust can get in. If it sits above the maximum, the gland cannot be tightened enough to hold the cable securely, and the seal ring can tear or extrude. Getting the size chart right is therefore not a matter of convenience — it directly affects the IP protection rating, the pull-out resistance, and the long-term reliability of the installation.

What to Measure Before Checking the Chart

• The actual outer diameter (OD) of the cable, measured with calipers — not the diameter printed on the cable datasheet.
• The panel or enclosure wall thickness, which can affect thread engagement.
• The thread standard already cut into the enclosure (Metric, PG, or NPT).
• Whether the cable is round, flat, or multi-core, since this changes which seal type is required.

Metric Cable Gland Size Chart

Metric threads (designated M12, M16, M20, M25, and so on) are the most widely used standard in Europe and in most modern industrial equipment, including Bimed's Standard Cable Glands, Brass and Standard Cable Glands, Plastic ranges. The number after the "M" refers to the nominal outer thread diameter in millimeters, and the thread pitch is typically 1.5 mm for sizes up to M25, and 1.5 or 2 mm above that.

Clamping ranges vary slightly between product lines and materials, so the table above should be used as a general reference. Exact values for a specific series should always be checked against Bimed's Industrial Cable Glands product documentation before ordering, especially when working close to the top or bottom of a range.

PG Cable Gland Size Chart

PG threads (from the German "Panzergewinde", meaning "armored thread") are an older DIN standard still found on a large amount of legacy equipment and enclosures, particularly in older industrial panels. PG sizes do not correspond directly to a real physical dimension in millimeters — the number is a legacy designator, not the thread diameter — which is why PG and Metric glands of a similar number are not interchangeable without an adapter.

When retrofitting a Metric cable gland into an enclosure originally tapped for PG thread (or vice versa), the thread itself will not seat correctly even if the clamping range matches — a reducer or the correct thread variant must be ordered rather than forcing a mismatched thread.

NPT Cable Gland Size Chart

NPT (National Pipe Thread) is the tapered thread standard used across North America and in oil, gas, and petrochemical installations worldwide, including many Hazardous Cable Glands built to UL and CSA requirements. Unlike Metric and PG threads, NPT is tapered rather than parallel, which means the seal at the thread itself tightens progressively as the fitting is screwed in — sizing is expressed in fractional inches (e.g. 1/2" NPT, 3/4" NPT).

Because NPT is a tapered thread standard, an NPT gland should never be substituted with a same-numbered Metric or PG gland — the thread profile, taper angle, and sealing mechanism are fundamentally different, and mixing them will not seal correctly even if the panel hole happens to be close in size.

Metric vs. PG vs. NPT: Key Differences

How to Read a Cable Gland Size Chart Correctly

1. Measure the cable's actual outer diameter, not the datasheet value.
2. Identify the thread standard already present in the enclosure (Metric, PG, or NPT) — never assume.
3. Find the row where the measured cable diameter falls inside the clamping range, ideally near the middle rather than at the very edge.
4. Confirm the panel cut-out diameter matches the enclosure's existing hole, or that a new hole can be drilled to that size.
5. Check the required IP rating and material against the operating environment before finalizing the selection.

Once the correct size and thread are identified, pairing the gland with the right accessories — Reducing or Multihole Seals for non-standard and multi-core cables, a Locknut for secure panel fixing, and a Dome Plug for any entries left unused — completes the installation and keeps the enclosure's IP rating intact.

Frequently Asked Questions

Conclusion

A cable gland size chart is only useful when it is read against an accurately measured cable diameter and the correct thread standard for the enclosure. Metric, PG, and NPT glands are sized differently and are not interchangeable without an adapter, so confirming both the thread type and the clamping range before ordering prevents sealing failures, IP rating loss, and unnecessary rework. Once the right size and thread are confirmed, completing the installation with the correct seals, locknuts, and dome plugs ensures the enclosure keeps its intended protection level for the long term.