Put an M20 gland beside a PG13.5 gland and compare the columns. Cable range 6 to 12 mm on both. Thread outside diameter 20 and 20.4. Mounting hole 20 to 20.2 and 20.4 to 20.6. Thread length 8 on both, bonding length 22 on both, spanner 22 on both. Six numbers, one difference: the thread form. One is a 60 degree metric thread, the other an 80 degree PG thread, and neither will enter the other’s tapped hole.

That pair is the argument of this page. A part number is a key to one supplier’s price list, not a description of a part, and the letters that look most technical often carry the least engineering.

A Part Number Is a House Code

No international standard defines a cable gland part number. IEC 62444 defines what a gland must survive. The thread standards define what M20×1.5 means. Nothing defines what the letters after the dash mean, so every manufacturer invents them, and the same string can mean different things in two catalogues.

Our own pages make the point faster than any argument. The suffix -NP, which stands for nickel plated, also appears on stainless tables where nothing is plated. The same M16 thread is sold as M16-NC13, M16-NC13L and M16-NC15.8, three parts with three bores. One nylon table lists an M25 as “M25 -NFL”, with a space no string comparison will forgive. A code is a label a factory applied to a drawing, and labels drift.

The Five Blocks of a Gland Code

Almost every gland code on the market can be split into five blocks, even when the supplier would not describe it that way. Reading in this order stops the most common mistake, which is treating the size block as a description of the whole part.

Block One: the Thread, and the Number That Is Not the Cable

The number in M20 is the thread outside diameter, not the cable size and not quite the hole either: the hole runs 20 to 20.2 mm, two tenths above the thread, and the seal does the sealing. A 20 mm cable is something else entirely. On this series M20 stops at 12 mm, so the answer to a 20 mm cable is a larger gland, not a longer thread.

Four thread systems appear on our nylon range in one line: metric, PG, G (PF) and NPT. They are not variants of each other. Metric is a 60 degree thread to EN 60423. PG is an 80 degree form whose numbers are neither the diameter nor the hole, as our PG and metric comparison sets out. G, or PF, is a parallel pipe thread that seals on a face or an O-ring rather than on the thread. NPT is tapered at 1:16 and seals on the threads themselves. A PG13.5 code and an M20 code describe parts that will not interchange, and the dimensional tables will not warn you, because on the numbers they are the same size.

Block Two: the Family Letters

The letters in front of the size are the part of the code most often skipped and the part that changes what the object is. On our pages, N- marks the standard nylon gland, NLM a split or unified nylon body, NLWM the 90 degree elbow, L a long thread, NFL a flexible nylon gland, and NC a watertight conduit fitting. The brass series carries no family letters, because there is only one body shape.

The elbow is the clearest case. NLWM20×1.5 and M20-NP share a thread, a hole and a cable range, and they are not interchangeable, because the elbow adds 43 mm of height above the panel that has to clear whatever sits beside it. A code without the W would tell a buyer everything except the one dimension that decides the installation.

Block Three: the Suffix Is Where the Part Lives

Two glands with the same thread, hole and cable range can differ by six millimetres of thread length, by a contact spring, or by a split body that fits over a terminated cable. All of that lives in the suffix, which deserves more attention than the size.

The long-thread case is worth holding on to. N-M12 gives a thread length of 9 mm and M12-L gives 15 mm, on the same thread, the same hole and the same cable range. If your panel plus washer plus locknut stack needs 12 mm, the standard part cannot be made to work by tightening it harder, and the -L is the whole difference between an assembly and a leak.

The Pitch Everyone Drops

The pitch is the one part of the code that is routinely omitted, because 1.5 mm is the default across most of the metric range and habit fills in the gap. It is not universal. M8 uses 1.25 on our nylon series, and G and NPT threads are specified on entirely different conventions, NPT in threads per inch rather than millimetres. A supplier receiving an order for M8 without a pitch will supply their default, which will usually be right and occasionally will not.

Two threads of the same diameter and different pitch look identical at arm’s length and will start to engage, which makes the error expensive: it survives a visual check and fails at the first pressure test.

Same Code, Different Gland

This is where the code does real commercial damage. An M20-NP from one factory and an M20-NP from another can differ in every dimension that matters while both being honestly described. The drilling is the same, so both will fit the panel. Nothing else is guaranteed.

A second-order test catches most of these before they reach a panel: does your existing accessory still fit? A locknut cut to another maker’s thread form will start on two or three threads and then bind. The part that gives it away is never the gland, it is the nut.

The Four Fields an Order Line Needs

A reorderable line is not a code. It is a code plus the three dimensions the code omits, written the same way every time so that a new buyer can use it without a phone call.

For a project order, add the IP statement with depth and duration and the elastomer, and the line stops being ambiguous. That is also the point at which a supplier can quote accurately instead of quoting the closest thing in stock.

Keep a House List, Not a Memory

The failure this page is really about is not a wrong order, it is a right order that cannot be repeated. The person who knew that “the small nylon one with the long thread” means M12-L leaves, and the next buyer orders N-M12, which arrives with 9 mm of thread instead of 15. A house list fixes it in one page per part: code, the dimensional row it maps to, a photograph, the supplier, the date, and one physical sample in a box. Six lines per part, and it survives catalogue redesigns in a way the code does not.

Reading a Gland You Cannot Identify

When the code is gone, worn off, or from a supplier that no longer exists, the part can still be identified, but only by measurement rather than by guessing at letters. Measure the thread outside diameter across the crests. Count the turns over 10 mm to establish the pitch, or use a thread gauge. Measure the hole it came out of. Measure the cable range at the insert, not at the body.

Two measurements decide it. A 20.0 mm thread with a 1.5 pitch is M20; 20.4 mm is PG13.5, whatever the markings suggest, and a calliper sees the difference a photograph hides. Where the two are a tenth apart, test-fit a known locknut: the accessory is a faster thread-form gauge than any table.

Часто задаваемые вопросы

What does the NP in M20-NP mean?

Nickel plated, in our catalogue. It is a house convention, not a standard, and it shows why a code needs its catalogue: the same suffix appears on stainless pages, where there is no plating.

Is a cable gland part number standardised anywhere?

No. Thread designations are standardised and the product standard defines what a gland must survive, but the part number is invented by each manufacturer. Two suppliers using the same string promise nothing.

Can I replace a PG gland with a metric one of the same size?

Only if the panel is being re-drilled or the hole is a plain clearance hole with a locknut. A tapped PG hole will not accept a metric thread, and the thread forms are 80 degrees against 60, so they will start and then bind rather than seat.

Why does the same code come with different cable ranges?

Because cable range is a property of the clamping insert, and inserts vary between manufacturers and between product families. The thread is fixed by the standard; the insert is a design choice, so the range has to be quoted rather than inferred.

What is the most common ordering mistake with these codes?

Ordering by the size block alone. M20 tells you the hole and nothing about the cable, the thread length or the finish, and those three are what a project actually fails on.

If you have a code you cannot decode, or a panel hole and a cable and no clear idea which gland belongs between them, send us the thread size and the cable diameter. Our guide to gland types, the nylon series and the brass M20 series cover the two families most orders come from.