PG29 Cable Gland Size Guide

November 4, 2026 8 minutes

PG29 is where a cable gland stops behaving like a threaded bushing and starts behaving like a structural part. It grips an 18 to 25 mm cable, passes through a hole a fraction over 37 mm, and presents a 40 mm hex to whatever tool is on site. All three are large enough to set the panel layout before anything is ordered.

This page gives the published dimensions, the PG ladder PG29 sits in, and the three metric threads that clamp the same cable into three different holes. For the whole series see the cable gland thread size chart.

What a PG29 Gland Is

PG29 is a straight entry gland: a rubber insert compressed onto the sheath by a dome nut, and a face washer under a locknut sealing against the enclosure. It exists in nickel-plated brass and in 304 or 316 stainless steel with identical mounting dimensions, so a material change late in a project does not move the hole.

What separates it from the small sizes is proportion. The thread is 37 mm across, the body holds a 31 mm bonding length, and the insert closes onto a sheath stiffer than anything below M25. At this size the questions are about the panel and the tool, not the cable.

The Dimensions That Decide Fit

Parameter	PG29 value	What it decides
Thread	PG29, 80 degree PG form	Not interchangeable with M37 despite the same outside diameter
Cable range	18 to 25 mm	Measured sheath diameter at its largest point, not the nominal size
Thread outside diameter	37 mm	The figure the hole is cut against
Mounting hole	37 to 37.2 mm	Thread outside diameter plus 0.2 mm, as across the range
Thread length GL	11 mm	Must exceed wall plus washer plus locknut plus any tag
Bonding length	31 mm	Insert travel; sets how much sheath ends up inside the body
Spanner size	40 mm	The same wrench as M36, M37 and M40

Where PG29 Sits in the PG Ladder

Above PG21 the PG series gets coarse. The bands do not slide up a millimetre at a time the way the metric series does.

Size	Cable range	Thread O.D.	Mounting hole	GL	Spanner
PG21	13 to 18 mm	28.3 mm	28.3 to 28.5 mm	9 mm	30 / 32 mm
PG25	15 to 22 mm	32 mm	32 to 32.2 mm	10 mm	35 mm
PG29	18 to 25 mm	37 mm	37 to 37.2 mm	11 mm	40 mm
PG36	25 to 33 mm	47 mm	47 to 47.2 mm	12 mm	50 mm

Only one overlap exists in this part of the series: PG25 and PG29 both cover 18 to 22 mm, which is the single place where two glands suit the same cable. Everywhere else the step is hard, and 26 mm belongs to PG36 with no argument.

The hole jumps faster than the cable does. From PG29 to PG36 the thread grows by 10 mm while the bottom of the band stays at 25 mm, so one extra millimetre of cable can cost a new gland plate.

The Same Cable, Four Threads, Three Holes

The 18 to 25 mm band is served by one PG size and three metric ones, and the metric three differ only in the hole you are willing to cut.

Size	Cable range	Thread O.D.	Mounting hole	GL	Spanner
M36 x 1.5	18 to 25 mm	36 mm	36 to 36.2 mm	10 mm	40 mm
M37 x 1.5	18 to 25 mm	37 mm	37 to 37.2 mm	10 mm	40 mm
PG29	18 to 25 mm	37 mm	37 to 37.2 mm	11 mm	40 mm
M40 x 1.5	18 to 25 mm	40 mm	40 to 40.2 mm	11 mm	40 / 45 mm

PG29 and M37 share a mounting hole almost exactly, which helps in one direction only. A plain clearance hole at 37 mm passes either thread, so a PG site and a metric site can use the same drilled pattern with different locknuts. A tapped hole cannot be shared: it was cut to one thread form and the other will not run into it.

Read the hole, not the drawing. A pressed-steel enclosure already punched at 36 mm takes M36 and will not take PG29; one punched at 37 mm by someone who assumed M37 takes PG29 with a locknut, which is often the cheapest way to keep a PG standard on a panel drawn in metric.

Eleven Millimetres of Thread and the Wall Stack

GL on PG29 is 11 mm, about 0.30 of the thread diameter. That is the last size where the ratio reads comfortably: PG36 drops to 0.26 and PG63 to 0.21, and above this point the wall stack starts deciding where a gland can go rather than what size it is.

Wall thickness plus flat washer plus locknut plus any earth tag has to come in under 11 mm. At 37 mm the plate is usually a machined gland plate of several millimetres rather than thin sheet, and a locknut at this size is a thick part, so the sum closes faster than it does at M20. If it is over, the answers are a longer thread, a different entry position or a counterbore, not a stack of washers, which moves the seal off the face it was designed for.

Setting the Hole and the Bearing Face

The hole is 37 to 37.2 mm, and the 0.2 mm is clearance rather than adjustment. A hole at 38 mm will bolt up and still leak, because the washer seals on the face and not in the bore, and the extra clearance lets it extrude instead of compress.

The bearing face is what gets ignored at this diameter. A 37 mm hole saw leaves a breakout burr that a small washer would bridge and this one will not, and a rolled lip or a dished face becomes a leak that returns after every attempt to repair it. Deburr and check the face with a straight edge first.

At 37 mm the plate is usually machined rather than folded sheet. The washer seals on the outside face, the locknut clamps from inside, and everything in that stack is taken out of 11 mm of thread.

Spanner 40 and the Clear Swing

40 mm across flats is the same wrench that fits M36, M37 and M40, a small gain where a plant keeps one kit for a range of entries. The hex is deep enough at this size for a proper open-end wrench; an adjustable one rounds the corners before it turns the nut.

Access is the half of the problem that drawings never show. The wrench needs the hex plus an arc to swing it, and a gland plate with a row of entries is laid out to fit the glands rather than the tools. Where the arc is missing, the practical answer is to assemble gland, locknut and cable on the bench and fit the assembly, which reverses the normal order of work and belongs in the method statement.

A row of entries at this size is decided by the swing of the wrench, not by the pitch of the holes. The gap that looks generous on a drawing is often the one the tool cannot use.

The Cable Is Now a Load

An 18 to 25 mm cable is stiff and heavy, and the insert grips the sheath without carrying weight. That distinction decides whether the entry survives: the gland is a seal and the restraint belongs somewhere else. Support the cable within the run so the gland sees no axial pull, and route the first bend at the cable’s own minimum radius. The split between sealing and load bearing is in cable gland strain relief.

Bending is the other half. Force the cable off its natural line immediately past the dome nut and the washer unloads on one side, so the leak appears on that side only and reads as a faulty gland. It is not one; the cure is a longer first run or a different entry position.

Torque needs care here too. The lever is twice as long as on an M20, so the same hand force gives roughly twice the moment and can compress the insert past the point where it has travel left to follow thermal movement. Use the datasheet figure, or judge by a pull test rather than a nut turned until it stops; the reasoning is in the cable gland torque guide.

Material at 37 mm

Nickel-plated brass covers industrial enclosures and runs from -40 to +120 C. Stainless 304 or 316L goes to +200 C and answers chloride, washdown and coastal air. At 37 mm the couple between a brass gland and a steel enclosure is a large area, and the plating is thinnest where the thread is loaded.

Stainless into stainless brings galling instead, so the assembly needs a lubricant approved for the location. The marine PG29 body is 316 and uses the same hole, so the materials decision can be deferred without moving the pattern.

What to Put on the Purchase Order

Field	What to state	Why it matters
Thread	PG29, and the thread standard it is made to	PG29 and M37 share a diameter and not a thread form
Cable range	The measured sheath outside diameter, one figure	Inside the band is not the same as a good grip
Mounting hole	37 to 37.2 mm, or the plate detail	The hole is a clearance, not a fit
Thread length	GL 11 mm, or the wall stack it must clear	This is the first size where the stack bites
Material	Grade plus certificate, for example 316L with mill cert	Decides both the corrosion answer and the documents
Sealing	IP rating with depth and duration	IP68 on its own is not a specification
Accessories	Locknut, washer, earth tag as separate lines	Items described as “with gland” are often not in the carton

The smaller end of the family is in the PG13.5 size guide, the largest in the PG63 size guide, and the thread forms in PG versus metric cable glands. For a 22 mm cable the question is whether the size below will do, which the M25 size guide answers from the metric side. The part is listed as the PG29 stainless steel cable gland; the metric equivalent in brass is the M37 brass gland.

What size hole does a PG29 cable gland need?

37 to 37.2 mm. The hole is the thread outside diameter plus 0.2 mm, and drilling to the nominal 29 mm will not pass the gland at all.

What cable diameter does PG29 take?

18 to 25 mm sheath diameter. Measure at the largest point on the finished cable, and avoid landing a 25 mm cable at the top of the band where the insert has least travel left.

Is PG29 the same as M37?

The thread outside diameter is identical at 37 mm, so a plain clearance hole suits either. The thread form is not the same, so they cannot share a tapped hole, a locknut or an adapter.

Can I use PG25 instead of PG29 for a 20 mm cable?

Yes, that band is the only overlap in this part of the series. PG25 takes 15 to 22 mm through a 32 mm hole, so the choice is made by which hole suits the panel.

Is PG29 available in stainless steel?

Yes, in 304 and 316 or 316L, with the same thread outside diameter, mounting hole, GL and spanner size as the brass version. Only the temperature range and the corrosion behaviour change.