What “Spanner Size” Actually Measures

On a cable gland drawing, spanner size is the width across flats (WAF) of the hexagonal sections — the dimension a tool actually grips. It is not the thread diameter, and it is not the cut-out diameter. Those three numbers sit within a few millimetres of each other on the same gland, which is exactly why so many installation kits end up with a spanner that is one size out.

An M20 gland, for example, has a 20.0 mm thread, needs a 20.0–20.2 mm panel hole, and takes a 22 mm spanner on the body. Three numbers, one fitting, one millimetre or two apart. Read one of them as another and the job stalls at the enclosure wall.

The charts below cover every metric and PG size we produce, measured on our standard nickel-plated brass body. If you are replacing an unknown gland or building a tool list for a crew, the second table is the one you will come back to.

Spanner Size Chart: Metric Threads M14–M63

Where a single figure is listed, the body hex and the locknut hex are the same. Where two figures are separated by a slash, the first is the body hex and the second is the locknut — the pair is given rather than one number because both are needed to do the job with two tools.

Spanner Size Chart: PG Threads PG7–PG63

PG glands follow the same rule, but the numbers diverge from metric much earlier than most people expect. PG7 takes a 14 mm spanner — there is no metric gland in our range that small — and PG63 needs 78 mm, which is wider than any metric size we stock. The two families are not interchangeable at the tool level, let alone at the thread.

Thread, Cut-out and Spanner Size: Three Numbers People Confuse

This table is worth printing for the workshop wall. Each row is the same M20 gland described three ways, and each of the three numbers has a different job.

The practical consequence: a cut-out punched to the spanner size is 2 mm oversize and will not seal, while a spanner chosen from the thread size is 2 mm undersize and will not fit. Neither mistake is visible until the gland is already in the panel.

Why One Gland Lists Two Spanner Sizes

Body Hex and Locknut Hex Are Usually Different

The body is constrained by the thread and the sealing geometry; the locknut is constrained by how much material the wall thickness of a cheap nut can carry. Manufacturers solve those two problems independently, so the hexes often land on different sizes — 24/27 on M24 and M25, 30/32 on M30, 40/45 on M40, 50/52 on M48, 57/55 on M50, 64/68 on M63. A kit that carries only the body size will stop at the locknut.

Where the Second Number Comes From

On some drawings the second figure is not a locknut at all but a reduced hex on the dome nut, or the hex on an optional nickel-plated locknut sold separately. When the datasheet gives two figures, ask which component each belongs to before you buy a tool; the answer changes what you need in the bag.

What Changes the Spanner Size Between Two Glands of the Same Thread

Thread size fixes the thread, nothing else. Three factors still move the hex:

• Body family. A heavy duty gland has a thicker wall and a larger sealing nut than a standard gland of the same thread, so its hex grows by one or two steps.
• Material. Stainless steel bodies are often cast or machined with slightly more material around the hex than brass, and 316L glands commonly sit one step above the brass figure for the same thread.
• Manufacturer. There is no standard that fixes the hex for a given thread. Two suppliers can both be correct with M20 bodies that take 22 mm and 24 mm spanners.

That last point is the one that costs money on a retrofit. Never order tools from the thread size alone — check the spanner size on the datasheet of the gland you are actually installing.

Three Glands Called M20 That Take Three Different Spanners

An M20 standard brass gland takes 22 mm. An M20 heavy duty gland, with its thicker wall and larger dome nut, typically needs 24 mm on the body. And an M20 gland with a separate nickel-plated locknut will often ask for 27 mm on that nut while the body stays at 22 mm. All three are correctly described as M20×1.5, all three fit the same 20.0–20.2 mm hole, and all three need different tools.

Choosing the Right Tool

An open-end spanner is the default. Use the hex that sits fully on the flats, keep the handle plane perpendicular to the axis, and apply force on the handle rather than pulling the gland sideways — a gland loaded off-axis compresses its insert unevenly and leaks at the thin side.

An adjustable wrench is acceptable on brass for low-torque work if the jaws are tight and square, but it will round the hex on stainless and it cannot be trusted where a torque figure matters. A six-point socket is the better answer for stainless and for anything you intend to torque, because it loads all six flats at once. Strap wrenches belong on the round dome nuts of small nylon glands, where there is no hex to grip at all.

Flats, Not Corners: Measuring a Gland in Your Hand

If you have the old gland but no datasheet, measure across two opposite flats — not corner to corner. Corner-to-corner on a hex is roughly 15% larger, which is enough to send a 22 mm gland to a 25 mm spanner and round it on the first turn. Measure the locknut separately; it is frequently the odd one out.

How Spanner Size and Tightening Torque Fit Together

The spanner is a lever, so the hex size and the torque figure are one decision rather than two. A 22 mm hex on a PA66 body will tolerate far less torque than the same 22 mm hex on brass, and the small sizes are where the difference matters: on PG7 and M14 the gap between sealed and stripped is a fraction of a turn.

Our per-size torque figures for PA66, nickel-plated brass and stainless steel bodies are listed in the split cable gland assembly data and explained in the cable gland torque guide. Use the torque guide for the method and this page for the tool. If you are still choosing the fitting itself, the guide to cable gland main types puts the families side by side, and the thread size chart covers cut-outs and thread lengths for the same sizes.

Spanner Sizes for Stainless and Heavy Duty Bodies

Treat the charts above as the brass baseline. For stainless steel and heavy duty variants, take the brass figure for the same thread and expect to go one step up — and confirm it on the drawing rather than assuming. If you are ordering glands and tools together, send us the thread list and we will return the hex for each line item, so the crew is not improvising with an adjustable wrench on a stainless body at height.

FAQ

What size spanner does an M20 cable gland need?

22 mm on the body for our standard nickel-plated brass M20×1.5 gland. Heavy duty M20 bodies usually take 24 mm, and a separate locknut on the same gland can be 27 mm. Check the datasheet for the exact variant before you buy the tool.

Is PG13.5 the same as M20 for tools?

No. PG13.5 takes a 22 mm spanner on our standard body, which happens to match M20, but its thread outside diameter is 20.4 mm against 20.0 mm and it needs a 20.4–20.6 mm cut-out. The tool may be the same; the hole is not.

Can I use an adjustable wrench on a cable gland?

On brass, at low torque, with jaws that sit flat on both faces — yes. On stainless steel it will round the hex, and anywhere a torque figure applies the reading becomes meaningless. Use a six-point socket for stainless and for torqued joints.

Why does my 22 mm spanner not fit an M20 gland?

Because the gland is not a standard 22 mm body. Heavy duty construction, a stainless body, a different manufacturer’s hex standard, or a locknut rather than the body will each explain a 24 mm or 27 mm requirement on a gland that is still correctly called M20.

Do stainless steel glands use the same spanner as brass?

Usually one size up. Stainless bodies carry more material around the hex and are often machined to a larger flat. Confirm on the drawing — and never open a stainless hex with an adjustable wrench.

Key Takeaway

Spanner size is the width across flats, and it is the only one of the three gland dimensions that describes the tool rather than the hole. Read it from the datasheet of the exact variant you are installing, allow for a different locknut hex, and buy the socket for stainless. Everything else on the gland follows the thread; the tool follows the hex.