Quick Answer: Cable gland thread types fall into four families: metric (60°, 1.5 mm pitch, parallel), PG (80° flank, legacy German), NPT (60°, tapered, seals on the thread) and BSP (55° Whitworth, parallel G or tapered R). Measure the outside diameter, read the pitch, and check the flank angle with a gauge before you fit anything. A good cable gland supplier India teams can phone will confirm the thread first. For cable gland thread types India sites meet most, expect M20, M25, PG13.5 and 1/2″ or 3/4″ NPT.

Introduction

A machine lands at the plant gate with a German nameplate and a row of unfamiliar entries. The commissioning crew grabs M20 glands from the store. One goes in easily for three turns, then locks. Someone fetches a longer spanner.

That is how a thread mismatch starts. It ends as a stripped enclosure, a leaking entry and a lost afternoon.

We work as a cable gland supplier India maintenance teams and OEM service desks call when this happens. As a metric cable gland supplier Delhi buyers can visit in Chawri Bazar, we have learned that the gland rarely fails. The thread decision fails, usually before the gland is even opened. This guide gives you the numbers, the field tests and the traps that catalogue pages skip.

We sell Dowells, Comet and HMI in the high range, and Diamond and MIC in the medium range. Every one of them still has to screw into something. So start with the thread.

Why the Thread Is the First Check for a Cable Gland Supplier India Buyers Can Rely On

Most people choose a gland by cable diameter. That is the correct second step. The correct first step is the entry.

Indian plants run mixed fleets. A single shop floor can hold a Taiwanese press with metric entries, a German packaging line with PG holes, a US-built skid with NPT junction boxes, and a forty-year-old Indian motor with a BSP terminal box. One store drawer of glands will not cover all four.

A wrong-thread gland causes damage that hides well. It passes the hand test. It survives commissioning. It fails at the first monsoon or the first washdown, because the seal never had a proper surface to work against. The IP rating on the box becomes fiction, earth continuity through the thread goes unreliable, and in a hazardous area the certificate no longer describes what is installed.

Three facts make the problem worse.

• Size names mislead. PG13.5 is not 13.5 mm. A 1/2″ NPT thread is not 12.7 mm. Only the metric name tells you the real diameter.
• Several sizes sit within one or two millimetres of each other across standards. Your fingers cannot tell them apart.
• Conversion charts online often match cable range, not thread. We cover that trap later.

The Four Standards at a Glance

Here is the comparison we keep on the counter.

Feature	Metric (ISO)	PG (DIN 40430)	NPT	BSP
Flank angle	60°	80°	60°	55°
Form	Parallel	Parallel	Tapered, 1:16	G is parallel; R and Rp are tapered
Size name	M20 x 1.5 (diameter x pitch, mm)	PG13.5 (nominal number, not mm)	1/2″ (nominal pipe size)	G 1/2 (nominal pipe size)
Typical pitch	1.5 mm on every gland size	1.27 to 1.59 mm	1.81 mm at 1/2″ and 3/4″; 2.21 mm from 1″	1.81 mm at 1/2″ and 3/4″; 2.31 mm from 1″
Where it seals	Washer or O-ring under the flange	Washer or O-ring under the flange	On the thread flanks, with sealant	G: washer. R and Rp: on the thread
Status	Current standard for glands	Withdrawn, still common on imported machines	Standard on US-origin equipment	Common in Indian pipework and older switchgear
Common risk	Fine pitch cross-threads in soft castings	Mistaken for M20 or M25	Mistaken for BSP at 1/2″ and 3/4″	Marking ambiguity (G or R?)

Keep the table in mind. The next sections explain why each cell matters.

Metric Cable Gland India: What M20 x 1.5 Really Means

Metric is the only system that names itself honestly. M20 x 1.5 means a 20 mm outside diameter and a 1.5 mm pitch. That is all you need to measure it with a caliper and a pitch gauge.

Gland makers follow a short ladder: M12, M16, M20, M25, M32, M40, M50 and M63, all at 1.5 mm pitch. European practice ties these to EN 60423 for the thread and EN 50262 for the gland. Because the pitch never changes, a locknut, a blanking plug and a gland of the same size interchange freely. That sounds minor. On a maintenance shelf it saves you from a dozen near-miss parts.

When buyers search for a metric cable gland India sites can stock in volume, two details separate a good order from a bad one.

The thread does not set the cable range.An M20 entry takes glands for a window of cable diameters, and the window shifts between makers and between brass, nylon and stainless bodies. Read the datasheet range, not the thread, and measure the actual cable over its outer sheath. Our guide to nickel-plated brass vs nylon vs stainless steel glands shows how body material changes that range.

Fine pitch punishes carelessness.A 1.5 mm pitch is shallow. Cast aluminium boxes and thin sheet metal tapped holes strip fast when a crew drives a gland with a power tool. Start every gland by hand. If it will not spin freely for at least three full turns, stop.

On a clearance hole with a locknut, the metric hole is about 20.5 mm for M20 and 25.5 mm for M25. The hole tells you nothing about the thread, which is exactly why a wrong locknut gets through unnoticed.

PG Thread Cable Gland: The Legacy Standard That Will Not Disappear

PG stands for Panzergewinde, armoured-conduit thread. German engineers designed it under DIN 40430 for thin-walled steel conduit. The wall was thin, so the thread is shallow, and the flank angle opens to 80° to give it strength. That wide flank is the fingerprint of PG. Metric and NPT both use 60°.

Then the standard was withdrawn. A metric fine thread with 1.5 mm pitch replaced it, and glands moved to M-sizes. But the machines built under PG did not retire. German and Italian packaging lines, textile machines, sensors on reactors and many control boxes still carry PG entries today. Indian plants inherit them with every second-hand import.

The core numbers, from the standard:

• PG7: 12.5 mm outside diameter, 1.27 mm pitch
• PG9: 15.2 mm, 1.41 mm
• PG11: 18.6 mm, 1.41 mm
• PG13.5: 20.4 mm, 1.41 mm
• PG16: 22.5 mm, 1.41 mm
• PG21: 28.3 mm, 1.59 mm
• PG29: 37.0 mm, 1.59 mm
• PG36: 47.0 mm, 1.59 mm
• PG48: 59.3 mm, 1.59 mm

Read the list again. The PG number loosely tracks the largest cable that passes through the conduit, not the thread diameter. That is why PG13.5 measures 20.4 mm and not 13.5.

There is a data trap here. Some marketplace listings publish a chart that equates PG7 with M16 x 1.5 and PG9 with M20 x 1.5. Those pairings match cable range, not thread. Real PG7 is 12.5 mm at 1.27 pitch. If you order an M16 gland for a PG7 entry because a chart said so, you will receive a part that cannot seat.

Nylon is the usual body for PG glands, because most PG entries sit on plastic enclosures and control boxes. We list a PVC PG gland range for exactly these repairs. A PG thread cable gland dealer Delhi NCR plants use should keep PG7 to PG21 in hand, since those cover most imported control cabinets.

NPT: The Taper That Seals Itself

NPT follows ANSI/ASME B1.20.1. It has a 60° flank and a taper of 1:16 on diameter, about 1°47′ per side. The thread gets tighter as it advances. Its crests and roots are flattened, so the flanks interfere and the joint seals with the help of PTFE tape or thread compound.

You meet NPT on US-origin skids, oil and gas packages, pumps, flameproof junction boxes and conduit-based installations. The common sizes are 1/2″, 3/4″, 1″, 1-1/4″, 1-1/2″ and 2″. The pitches are 14 threads per inch for 1/2″ and 3/4″, then 11.5 for 1″ and above.

Sealing logic differs from every other family here.

An NPT gland needs no sealing washer. The thread does the work. Wrap two to three turns of tape in the thread direction, thread the gland by hand, then add roughly two turns with a spanner. Size and material change that number, so follow the maker’s guidance.

Sealant and earth continuity compete. PTFE tape insulates. On a metal gland that relies on the thread for bonding, a heavy tape wrap can break the earth path. Run a bonding jumper or earthing tag, as we explain in cable gland accessories, locknuts and earthing tags.

Taper loads the boss. A brass NPT gland driven into a plastic or die-cast boss acts like a wedge. It hoops the wall outward and cracks it, sometimes weeks later. For plastic enclosures, use a parallel entry with an O-ring instead.

Watch for NPS or NPSM as well. Those are straight (parallel) pipe threads with the same nominal names. A drawing that says “1/2 NPS” wants a washer, not tape.

Forteams hunting an NPT cable gland Delhi stockist for skid and pump work, send the thread name and the enclosure material. The material decides the entry style.

BSP: Two Standards Hiding Under One Name

British Standard Pipe is a Whitworth thread with a 55° flank and rounded crests. It splits into two systems that share a name and little else.

• G (parallel)under ISO 228-1. It seals with a washer or bonded seal, like metric.
• R and Rp (tapered)under ISO 7. The taper matches NPT at 1:16, but the angle does not. These seal on the thread.

India’s pipe thread standards mirror these two systems, so BSP shows up on older Indian switchgear, motor terminal boxes, pumps and some flameproof enclosures. Engineers say “half-inch BSP” and mean either family.

The drawing often says “1/2 BSP” with no letter. Ask. A parallel G thread needs a washer and gets no tape. A tapered R thread needs tape and gets no washer. Guess wrong and you build a leak path at the exact joint you wanted to seal.

Typical diameters: G1/2 measures 20.96 mm, G3/4 26.44 mm, G1 33.25 mm, G1-1/4 41.91 mm and G1-1/2 47.80 mm. Keep those numbers; they matter in the next section.

The Look-Alike Trap: Threads That Start Together and Then Fail

This section holds the data most catalogue pages leave out. Put the major diameters side by side and four “families” appear. Inside each family, threads from different standards sit within a couple of millimetres of each other.

Family	Metric	PG	NPT (at mouth)	BSP (G)
About 20 mm	M20: 20.0 mm	PG13.5: 20.4 mm	1/2″: 21.3 mm	G1/2: 21.0 mm
About 26 mm	M25: 25.0 mm	PG21: 28.3 mm	3/4″: 26.7 mm	G3/4: 26.4 mm
About 33 mm	M32: 32.0 mm	none	1″: 33.4 mm	G1: 33.2 mm
About 42 mm	M40: 40.0 mm	none	1-1/4″: 42.2 mm	G1-1/4: 41.9 mm
About 48 mm	M50: 50.0 mm	PG36: 47.0 mm	1-1/2″: 48.3 mm	G1-1/2: 47.8 mm

Now the engineering behind why these fail.

PG13.5 and M20. Their pitches differ by only 0.09 mm (1.41 against 1.50). Over three turns the offset is under 0.3 mm, so the gland starts without protest. Then the 80° flanks meet 60° flanks and the thread jams. The direction matters. A PG13.5 male has a 20.4 mm major diameter, bigger than an M20 female, so it is forced in and cuts. An M20 male runs 0.4 mm under a PG13.5 female, so it spins in loosely with shallow engagement and leaks later. One fails loudly. The other fails quietly.

1/2″ NPT and G1/2. Both run 14 threads per inch, a pitch of 1.81 mm. Identical pitch lets the parts start, and the 5° flank gap lets them bind. The pitch gauge will not warn you here, because the leaf fits the pitch. Only the angle test, with the leaf held against light, shows the gap.

M25 and 3/4″ NPT. An M25 male is 1.7 mm smaller than the NPT opening. It drops in, grips only the deepest one or two threads where the taper narrows, and looks installed. In a flameproof box that leaves far fewer engaged threads than the certificate demands.

How to Identify an Unknown Entry in Five Minutes

You do not need a lab. You need a caliper, a thread pitch gauge set and ten minutes. A good cable gland supplier India teams trust can confirm the answer from a photo and three numbers.

1. Clean the thread.Remove paint, sealant and swarf with a brush and solvent. Dirt adds a false reading.
2. Measure the outside diameter at three points along a male thread, or read the bore of a female thread near the mouth. If the diameter changes along the length, you have a tapered thread (NPT or R). If it stays constant, the thread is parallel.
3. Match the pitch. Use a metric leaf for 1.5 mm. Use an inch leaf for 14, 11.5 or 11 threads per inch. A 1.41 mm pitch points to PG.
4. Check the flank angle. Press the gauge leaf into the thread and look for light behind it. A perfect match shows no gap. A 55° leaf in a 60° thread rocks and shows a sliver of light.
5. Confirm with a master. Keep a small shelf of known-good glands: M20, M25, PG13.5, PG16, PG21, 1/2″ NPT, 3/4″ NPT, G1/2 and G3/4. Mark them as gauges. Try the master by hand. It should run freely for at least three turns with no wobble.

Write the result as a full designation: “M20 x 1.5 parallel”, “1/2″ NPT”, “G1/2 parallel”. Never write “20 mm thread” or “1/2 inch”. Those phrases point to three different standardsat once.

Sealing: Parallel and Tapered Threads Need Different Logic

Engineers carry one idea from plumbing to electrical work that fails here: seal everything with tape. Do not.

Metric, PG and G threads are parallel. The thread holds the gland in place, nothing more. The seal lives at the shoulder, where a washer or O-ring squeezes between gland flange and enclosure face. Tape on that thread does nothing useful. It can even stop the flange from seating square.

Two details matter at the seat. First, check flatness. A dished or dented gland plate lets the washer extrude on one side. Second, watch the paint. Powder coat under a washer creeps with time and heat, torque relaxes, and the joint weeps. On painted panels, mask or scrape the seating ring and use a gland with an earthing tag. For the numbers that keep the joint tight, read our post on cable gland torque and why over-tightening fails more joints.

Tapered threads reverse the logic. NPT and R threads seal on their flanks, so you apply sealant and skip the washer. Pulling them tighter to chase a drip only deepens the wedge and splits the boss.

One rule covers both: choose the entry method first, then the gland. Your IP66 or IP68 claim lives or dies on that choice, not on the printed rating on the carton.

Hazardous Areas: Thread Engagement and Certificates

In a flameproof (Ex d) enclosure the thread is part of the flame path. Standards for flameproof enclosures call for a minimum number of engaged full threads, typically five, and the entry must match the thread named on the certificate. A loose M25 in a 3/4″ NPT hole fails that test even when it looks tight.

Three practical rules follow.

• Use only glands and adapters certified for that enclosure and thread. A generic adapter voids the arrangement.
• Read the certificate for the thread form and for sealant limits.
• Verify full engagement by counting turns, not by feel.

Our post on flameproof Ex d cable glands, PESO and IECEx certification goes through the paperwork. Armoured cable adds another variable, covered in armoured vs unarmoured cable glands.

Customer Problems and Solutions

These are the six situations service teams describe most often.

Problem 1: The German machine with PG13.5 holes.

The store has only M20 glands, so the crew fits M20 anyway. The seal weeps and the nylon locknut slips.

Solution: Order true PG13.5 glands and PG locknuts. If the plate belongs to you and has enough wall, re-punch the holes to M20 and fit metric throughout. Do not mix.

Problem 2: A US skid with 3/4″ NPT entries in flameproof boxes.

Metric glands go in, look tight and fail inspection.

Solution: Fit 3/4″ NPT glands, or a certified adapter listed for that box. Count engaged threads and record them.

Problem 3: The 1/2″ mix-up.

A crew drives a 1/2″ NPT gland into a G1/2 motor terminal box. It starts, binds after four turns and galls the brass.

Solution: Run the pitch-and-angle test before ordering. Replace the damaged female thread or the box, and fit a G1/2 gland with a bonded seal.

Problem 4: A cracked plastic boss.

A brass NPT gland split a polycarbonate junction box within days.

Solution: Replace the box entry with a parallel metric or PG gland and an O-ring. Our comparison of nylon and brass cable glands for outdoor enclosures helps you pick the body.

Problem 5: A mixed gland plate on a VFD retrofit.

Old holes are PG, new drives need shielded cable, and the plate now carries three thread systems.

Solution: Standardise the plate on metric. Use EMC glands for VFD cables with full-circle shield contact, and keep the PG plate as a spare.

Problem 6: The marketplace chart that sent the wrong spares.

A PG-to-metric chart showed PG9 as M20. The parts arrived and did not seat.

Solution: Throw the chart away. Measure the entry, read the full designation, and confirm with your supplier before ordering.

Adapters and Reducers: When They Help and When They Hurt

Adapters convert one thread to another, for example PG13.5 to M20 or 1/2″ NPT to M20. They solve real problems on legacy equipment you cannot modify.

They also add a joint. Each added interface is another place to leak, adds length, and in a hazardous area needs its own certification. Use an adapter when the enclosure belongs to someone else, or the unit is certified and cannot be re-tapped. Change the entry when the plate is yours and the wall is thick enough to tap.

Sheet metal walls of 1.5 to 3 mm give poor thread engagement. Use a clearance hole and a locknut instead of a tapped hole. Tapping thin metal looks neat and holds badly.

What to Send Your NPT and PG Cable Gland Supplier India Before You Order

A tight enquiry saves two rounds of calls. Send these eight items.

• Full thread designation, including parallel or tapered (for example, “G1/2 parallel”)
• Measured outside diameter and pitch, with a photo of the gauge in the thread
• Enclosure material and wall thickness
• Cable outer diameter, measured over the sheath
• Armoured or unarmoured cable
• Required IP rating
• Hazardous area details and certificate, if any
• Quantity, body material (brass, nylon or stainless) and any earthing tag requirement

That list lets us match a gland from our high range (Dowells, Comet, HMI) or medium range (Diamond, MIC) without guesswork. Our cable gland product range shows what we stock.

Cable Gland Supplier India Contact and Trust Details from Chawri Bazar, Delhi

Thunderbolt Electromech India Pvt. Ltd. supplies industrial plants, panel builders and OEM service teams across India. As a metric cable gland supplier Delhi customers can visit, and as a PG thread cable gland dealer Delhi NCR maintenance crews call for urgent repairs, we also supply NPT cable gland Delhi buyers need for imported skids and pumps.

• Brands:Dowells, Comet and HMI (high range); Diamond and MIC (medium range)
• Address:Shop no 3538, Sitaram Bazar Rd, Bazar Sirkiwalan, Chawri Bazar, Chandni Chowk, Delhi, 110006
• Phone:+91-9911886655, +91-6391217408
• Email:info@thunderboltelectromech.com, thunderboltelectromech@gmail.com
• Open hours:Monday to Saturday, 11:00 to 19:00

Bring a sample if you can. A gland in the hand beats a description on the phone. For more guides, see our full cable gland blog category, and read our pillar guide, Cable Gland Supplier India: 15 Expert Tips to Choose the Right Cable Gland for Industrial Projects.

FAQ: Cable Gland Thread Types

These are the questions engineers keep asking on Google, Reddit and Quora.

What is the difference between PG and metric cable gland threads?

A PG thread has an 80° flank and a pitch of 1.27 to 1.59 mm. Metric has a 60° flank and a constant 1.5 mm pitch. PG sizes are nominal numbers, while metric sizes are real diameters in millimetres.

Is PG13.5 the same as M20?

No. PG13.5 measures 20.4 mm at 1.41 mm pitch with an 80° flank. M20 measures 20.0 mm at 1.5 mm pitch with a 60° flank. They look close and start together, then bind or leak.

Can I use an M20 gland in a PG13.5 hole?

On a clearance hole, the hole size is nearly the same, but the locknut and thread differ, so use a PG gland or a certified adapter. In a tapped PG13.5 hole the M20 spins in loosely with shallow engagement and cannot hold IP.

Is BSP the same as NPT?

No. BSP uses a 55° flank and NPT uses 60°. At 1/2″ and 3/4″ both have 14 threads per inch, so they start together and then jam. At 1″ and above the pitch also differs (11 against 11.5 threads per inch).

Do NPT cable glands need a sealing washer or tape?

NPT seals on the thread, so it takes tape or compound and no washer. Parallel threads (metric, PG, G) take a washer or O-ring and no tape.

How do I identify a cable gland thread?

Measure the diameter at three points to detect taper, read the pitch with a gauge, and check the flank angle against light. Confirm with a known master gland.

What does M20 x 1.5 mean?

The thread has a 20 mm outside diameter and a 1.5 mm pitch. That is a fine thread, which is standard for cable glands.

Is PG thread obsolete?

The standard was withdrawn and metric replaced it, but PG remains common on imported machines, control boxes and sensors. Plants still need PG spares for years.

Can I use PTFE tape on a metric gland?

Tape does nothing useful on a parallel thread, because the seal is at the flange. It can also spoil earth continuity. Use the washer or O-ring instead.

Which thread is best for flameproof Ex d entries?

The one on the certificate. Both metric and NPT appear in Ex d. Check engagement, the certified adapter list and sealant limits.

Why do 1/2″ and 20 mm glands get confused?

NPT 1/2″ is 21.3 mm, G1/2 is 21.0 mm, PG13.5 is 20.4 mm and M20 is 20.0 mm. Fingers cannot tell the difference, so gauge it.

Do I need an adapter if my gland has the wrong thread?

Use an adapter only when you cannot change the entry, and pick a certified one in hazardous areas. If the plate is yours, re-punch or re-tap and keep one standard.

Conclusion: Pick a Cable Gland Supplier India Teams Can Verify Threads With

The four cable gland thread types are not interchangeable, and they are not as different as catalogues suggest. Metric names itself honestly, PG hides behind a number, NPT seals on a taper, and BSP splits into two systems under one name. Diameters across them differ by a millimetre or two, so a hand test lies. A caliper, a pitch gauge and a flank-angle check tell the truth in ten minutes.

Match the thread first. Choose the gland second. Seal the way the thread demands.

That discipline saves money and uptime. A cable gland supplier India plants can rely on will ask for the thread designationbefore quoting. We do. Call or message Thunderbolt Electromech India Pvt. Ltd. at +91-9911886655 or info@thunderboltelectromech.com, send a photo of your entry, and we will help you match it to Dowells, Comet, HMI, Diamond or MIC.