Two numbers decide whether a gland seals: the outside diameter of the cable, and the thread of the hole it enters. This page gives you both for metric, PG, NPT and G threads — and explains why two glands with the same thread can accept different cables.
Most wrong glands are ordered because the cable was described by its cross-section. A 3-core 2.5 mm² cable tells you how much copper is inside it — it tells you nothing about how thick the finished cable is. Depending on the insulation and the jacket, that same 3×2.5 mm² cable can arrive at 9 mm or at 12 mm outside diameter.
The second mistake is assuming one thread size means one cable range. It does not. M20 describes the hole, not the cable. Manufacturers fit different inserts into the same M20 body, so published clamping ranges for M20 run from about 6–12 mm to 7–13 mm depending on the supplier and the variant — and both are correct M20 glands.
So the order is always the same: measure the cable, pick the thread that matches the hole you already have, then check the specific part number against its own datasheet before you cut anything.
Thread diameters follow the published standards. Clamping ranges are typical industry values and do vary by manufacturer and by insert variant.
Read this before you cut metal. The clamping ranges below are common industry figures, not a specification of any one part. Use them to sanity-check a hole or a cable, then confirm against the actual datasheet for the part number you are buying. Where a cable sits on the edge of a range, step up to the next size.
The IEC and European default. Diameter and pitch are written directly: M20×1.5 is a 20 mm nominal diameter on a 1.5 mm pitch.
| Thread | Cable range | Thread OD | Hole to cut |
|---|---|---|---|
| M12×1.5 | 3 – 6.5 mm | 12.0 mm | 12.2 mm |
| M16×1.5 | 4 – 8 mm | 16.0 mm | 16.2 mm |
| M18×1.5 | 5 – 10 mm | 18.0 mm | 18.2 mm |
| M20×1.5 | 6 – 12 mm | 20.0 mm | 20.2 mm |
| M22×1.5 | 10 – 14 mm | 22.0 mm | 22.2 mm |
| M25×1.5 | 10 – 14 mm | 25.0 mm | 25.2 mm |
| M32×1.5 | 15 – 22 mm | 32.0 mm | 32.2 mm |
| M40×1.5 | 18 – 25 mm | 40.0 mm | 40.2 mm |
| M50×1.5 | 32 – 38 mm | 50.0 mm | 50.2 mm |
| M63×1.5 | 37 – 44 mm | 63.0 mm | 63.2 mm |
A legacy German conduit standard, still widespread on European and imported machinery. The size number is not a diameter — PG13.5 does not mean 13.5 mm of anything. Read the table.
| Thread | Cable range | Thread OD | Hole to cut |
|---|---|---|---|
| PG7 | 3 – 6.5 mm | 12.5 mm | 12.5 mm |
| PG9 | 4 – 8 mm | 15.2 mm | 15.2 mm |
| PG11 | 5 – 10 mm | 18.6 mm | 18.6 mm |
| PG13.5 | 6 – 12 mm | 20.4 mm | 20.4 mm |
| PG16 | 10 – 14 mm | 22.5 mm | 22.5 mm |
| PG21 | 13 – 18 mm | 28.3 mm | 28.3 mm |
| PG29 | 18 – 25 mm | 37.0 mm | 37.0 mm |
| PG36 | 22 – 32 mm | 47.0 mm | 47.0 mm |
| PG42 | 30 – 38 mm | 54.0 mm | 54.0 mm |
| PG48 | 34 – 44 mm | 59.3 mm | 59.3 mm |
The North American tapered standard. Sizes follow nominal pipe size, not measured diameter. Because the thread is tapered it seals on the thread itself — a sealant is required and no face O-ring is used.
| Thread | Cable range | Thread OD |
|---|---|---|
| NPT ¼" | 3 – 6 mm | 0.540 in |
| NPT ⅜" | 3 – 7 mm | 0.675 in |
| NPT ½" | 6 – 12 mm | 0.840 in |
| NPT ¾" | 13 – 18 mm | 1.050 in |
| NPT 1" | 18 – 25 mm | 1.315 in |
| NPT 1¼" | 22 – 32 mm | 1.660 in |
| NPT 1½" | 30 – 38 mm | 1.900 in |
| NPT 2" | 34 – 44 mm | 2.375 in |
Parallel pipe thread to ISO 228, common on process, marine and hydraulic-adjacent equipment. It looks close enough to NPT to be confused in an enquiry, and the two do not interchange.
| Thread | Thread OD | Seals on |
|---|---|---|
| G ¼" | ≈ 13.2 mm | Face washer |
| G ⅜" | ≈ 16.7 mm | Face washer |
| G ½" | ≈ 21.0 mm | Face washer |
| G ¾" | ≈ 26.4 mm | Face washer |
| G 1" | ≈ 33.2 mm | Face washer |
| G 1¼" | ≈ 41.9 mm | Face washer |
| G 1½" | ≈ 47.8 mm | Face washer |
| G 2" | ≈ 59.6 mm | Face washer |
Clamping ranges for G thread vary widely by body length and insert — send us the entry and the cable and we will match it.
Enter the outside diameter of your cable and this will show every size in the reference tables that accepts it. It reads the same numbers as the tables above — it is a shortcut, not a second opinion.
Measure the finished cable — jacket included, armour included where present. Do not use the conductor cross-section.
Matching sizes will appear here.
Metric, PG and G are parallel threads: the clearance hole sits just above the nominal diameter and the thread is cut into it. NPT is tapered, so it is drilled to a tapping size and then threaded — drilling an NPT entry to the outside diameter will not work.
If your cable sits between two sizes, or your hole is already cut and you are not sure what thread it is, send us a photo of the entry next to a rule. We will identify it from the outside diameter and pitch.
Send those two numbers and we will come back with the size, the material and a part number — or tell you honestly that we do not make it.
