A PG9 cable gland is what you reach for when the cable is past control-wire size but nowhere near a motor lead: its seal grips anything from 4 mm to 8 mm. That band is also the most crowded one in any catalogue, which is why the size gets ordered wrong. Two metric sizes cover exactly the same 4 mm to 8 mm, and one of them is functionally identical to PG9 apart from a fraction of a millimetre of thread. This guide gives the five numbers that define a PG9 cable gland and explains the two places it fails on site: the mounting hole and the bottom edge of the cable band. Every dimension comes from this range’s published PG series specification.
The 9 in PG9 is a nominal conduit size, not a dimension you can put a caliper on. The thread outside diameter is 15.2 mm, and the hole it needs is 15.2 mm to 15.4 mm: the thread plus the usual clearance. Those two are what most buyers check, and they are only half the specification.
The remaining three decide whether the gland can be installed at all. Cable range fixes what it seals, thread length decides which wall it passes through, spanner size decides whether you can reach it. Read them in that order.
| Dimension | PG9 value | What it constrains |
|---|---|---|
| Cable range | 4 mm to 8 mm | What the insert can grip and seal; the cable must sit inside it, not on its limit |
| Thread outside diameter | 15.2 mm | Which hole the gland physically enters |
| Mounting hole | 15.2 mm to 15.4 mm | The hole to drill or punch; wider and the washer cannot bridge the gap |
| Thread length GL | 8 mm | Wall thickness plus washer plus locknut has to fit inside it |
| Spanner size | 18 mm across flats | Access for tightening, and the pitch you can use between adjacent entries |
| Longitud de enlace | 20 mm | Depth needed inside the enclosure behind the wall |
The 4 mm to 8 mm band is not unique to PG9. In the same catalogue the M14, PG9 and M16 entries all state 4 mm to 8 mm. Three threads, three holes, one cable band. The cable therefore cannot be what chooses between them, even though it is the only thing most people quote when they raise an enquiry.
| Size | Cable range | D.E. de la rosca | Mounting hole | Thread length GL | Spanner |
|---|---|---|---|---|---|
| PG7 | 3 mm to 6.3 mm | 12.5 mm | 12.5 mm to 12.7 mm | 7 mm | 14 mm |
| M14 | 4 mm to 8 mm | 14 mm | 14 mm to 14.2 mm | 7 mm | 17 mm |
| PG9 | 4 mm to 8 mm | 15.2 mm | 15.2 mm to 15.4 mm | 8 mm | 18 mm |
| M16 | 4 mm to 8 mm | 16 mm | 16 mm to 16.2 mm | 8 mm | 18 mm |
| PG11 | 5 mm to 10 mm | 18.6 mm | 18.6 mm to 18.8 mm | 8 mm | 20/21 mm |
M14 is the budget option of the band, with a 7 mm thread and a 17 mm spanner, so it will not clear a thick panel or a tight pitch. PG9 and M16 are separated by 0.8 mm of thread and nothing else worth mentioning. PG11 starts where PG9 ends.
Set the two rows side by side and five columns match: 4 mm to 8 mm cable range, 8 mm thread length, 20 mm bonding length, 18 mm spanner, same body. The only real difference is the thread, 15.2 mm against 16 mm.
That 0.8 mm decides the order. A 16 mm knockout will not seal a PG9: the thread drops through, the washer sits over a gap it cannot bridge, the body hangs off-centre, and the joint weeps on one side — usually on the first wet day rather than at commissioning. In the other direction a 15.2 mm hole will not accept an M16 at all. Cross-reference charts that print “M16 = PG9” describe the cable range, and the statement holds only while nobody looks at the hole.
So a PG9 enquiry that arrives with an existing panel is really a question about the hole. If it is already punched, the thread is fixed and the cable range is whatever that thread takes. If the hole is still on the drawing, PG9 becomes one of three interchangeable ways to seal the same cable, best chosen on thread length and access.
A 4 mm to 8 mm range does not mean every cable inside it is equally well served. At 4.0 mm or 4.5 mm the insert sits at the bottom of its travel: it touches the jacket but compresses very little, so sealing pressure and retention are weakest exactly where a small cable is most likely to be pulled. A PG7 covering 3 mm to 6.3 mm, or a moulded M12 covering 3 mm to 6.5 mm, puts the same cable near the middle of the band where the insert has room to hold.
The top edge behaves the same way: a cable measuring 8.0 mm to 8.5 mm should move up to PG11 rather than be forced into a PG9 whose insert is already fully compressed. Specify so the measured jacket lands in the middle half of the range, not on either endpoint.
Measure at three points around the circumference rather than trusting the size printed on the drum. A jacket that reads 8.2 mm one way can read 7.7 mm the other, and the gland seals on the smallest figure.
Thread length is the number that ends a project late. GL 8 mm has to cover the panel, the sealing washer and the locknut in that order, and whatever is left is the margin. On a 5 mm plate there is nothing left.
| Wall construction | Rough stack-up | Does GL 8 mm work? |
|---|---|---|
| 1.5 mm sheet, washer, locknut | 1.5 + 1 + 4 = 6.5 mm | Yes, with about 1.5 mm spare |
| 3 mm plate, washer, locknut | 3 + 1 + 4 = 8 mm | At the limit; no margin for a paint film or a second washer |
| 5 mm plate, washer, locknut | 5 + 1 + 4 = 10 mm | No; needs a long-thread variant or a thinner mounting point |
| 6 mm tapped plate, no locknut | 6 mm | Yes; the thread is the only thing in the wall |
| Insulated panel with a liner | Liner plus core plus washer | Depends on the liner; check it before drilling |
Tapped holes change the arithmetic, which is why the same gland can be right on one enclosure and wrong on the next. Where the wall itself is threaded, the thread only has to span the wall, and 8 mm is comfortable to about 6 mm of plate. Where it is a plain hole, the locknut takes its 4 mm out of the same 8 mm and usable wall thickness halves. Use the locknut thickness on the datasheet for the part you buy.
The same nominal size is a different hole depending on body material. The metal PG9 needs 15.2 mm to 15.4 mm. The moulded nylon M16 states 16.2 mm to 16.5 mm, because a moulded thread runs thicker at the root than a cut one, and nylon M12 needs 12.2 mm to 12.5 mm against the metal M12’s 12 mm.
The flexible version adds a third variable without changing the hole. A PG9 flexible body keeps the 15.2 mm thread and the 4 mm to 8 mm range, but the spanner goes from 18 mm to 19 mm because the neck and dome nut are bulkier. The panel drawing does not change; the layout around it does. Stainless keeps the metal dimensions, so a stainless steel PG9 gland drops into the same hole, while the brass M14 y brass M16 each need their own.
The consequence is a sequencing rule: material first, then hole, then drill. Done the other way round, a workshop ends up with a punched 16 mm hole, a delivery of PG9 glands, and a box of penny washers nobody will sign off.
18 mm across flats is the smallest size in the range that still gives a wrench something to hold. That matters at the layout more than at the gland: two entries need the spanner body plus a swing arc, not the hole plus a millimetre, so two PG9 glands on 20 mm centres cannot both be tightened.
The same wrench behaves differently by material. On metal the hex is deep and the thread limits torque. On a moulded body the hex is shallower and the plastic yields first, so the force that feels normal on brass rounds a nylon hex.
Four of the five patterns below are visible before anything ships.
| What happens on site | What caused it | What fixes it |
|---|---|---|
| The gland drops through the hole | A 16 mm hole drilled for an “M16 equivalent” | Re-drill to 15.2 mm to 15.4 mm, or switch the order to M16 |
| Water tracks in at the first rain | A 4.2 mm cable sitting at the bottom of the band | Move to PG7 at 3 mm to 6.3 mm, or re-specify so the cable sits mid-band |
| The locknut will not start | An M16 locknut supplied against a PG9 gland | Match the accessory to the 80 degree PG thread, not the metric one |
| The thread never reaches the nut | GL 8 mm against a thick plate plus washer plus locknut | Long-thread variant, or a thinner wall at the entry |
| The nylon hex rounds off | Metal-body tightening habit applied to a moulded body | Tighten to the datasheet figure and stop at seal contact |
None of these is a manufacturing fault. Each is a decision taken at the drawing or the purchase order, so the fix always costs more than the gland.
Two lines on a drawing prevent most of the failures above: the thread callout with its standard, because PG is an 80 degree thread and a metric nut will appear to fit before it strips, and the hole with a tolerance, 15.2 mm to 15.4 mm rather than “about 15”.
For the same eight columns across every thread system, the cable gland thread size chart covers the whole range. The mounting hole chart gives the hole tolerance for each size, and the difference between 80 and 60 degree threads is in PG versus metric cable glands. The next size up is the PG29 size guide.
4 mm to 8 mm jacket diameter. That is the sheath, not the conductor, and the seal works best when the measured diameter sits mid-band rather than at either end.
15.2 mm to 15.4 mm. The thread measures 15.2 mm, and the extra 0.2 mm covers thread tolerance and gives the washer a flat surface. A 16 mm hole is too large.
For the cable, yes: both cover 4 mm to 8 mm and share the same thread length, bonding length and spanner. For the panel, no: PG9 needs 15.2 mm where M16 needs 16 mm to 16.2 mm.
Only with an adapter or a washer wide enough to bridge the 0.8 mm gap, and neither is a good permanent answer. The gland sits off-centre under load and the seal becomes one-sided.
15.2 mm outside diameter. The 9 in the name is a nominal conduit size and does not correspond to any dimension you can measure on the gland.
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