Selecting the correct nylon cable gland size is one of the most important steps in creating a reliable cable entry system. However, it is also one of the most common sources of mistakes during electrical enclosure design, equipment assembly, and cable gland purchasing.

A buyer may request an M20 cable gland because the enclosure has an M20 threaded hole, only to discover that the selected gland cannot properly grip the cable. Another buyer may choose a PG13.5 gland based on an old machine specification but fail to check whether the actual cable diameter falls within the gland's clamping range.

The main reason for this confusion is simple:

Cable gland thread size and cable diameter are two different specifications.

An M20 nylon cable gland does not mean that it is suitable for a 20 mm cable. The “M20” refers primarily to the mounting thread, while the actual cable that can pass through and be sealed by the gland is determined by its cable clamping range.

Understanding this distinction is the starting point for choosing the correct cable gland.

This guide explains how to match cable diameter with gland size, how to understand Metric, PG, and NPT specifications, how to read a cable gland size chart, and how to avoid the sizing mistakes that can cause poor sealing, weak strain relief, difficult installation, or unnecessary equipment failures.

Why Correct Nylon Cable Gland Sizing Matters

Cable glands do much more than fill a hole in an electrical enclosure.

When correctly selected and installed, a nylon cable gland can help:

• Secure the cable at the enclosure entry

• Reduce mechanical stress on internal terminals

• Provide cable strain relief

• Limit unwanted cable movement

• Protect against dust and moisture

• Support the enclosure's required IP protection

• Protect the cable jacket from the edge of the mounting hole

• Improve installation consistency

All of these functions depend on dimensional compatibility.

If the cable is too small for the gland's sealing range, the seal may not compress properly.

If the cable is too large, it may be difficult or impossible to pass through the sealing element.

If the mounting thread is incorrect, the gland cannot be securely installed in the enclosure.

Correct sizing therefore requires buyers to verify two dimensions separately:

1. The cable outside diameter

2. The gland mounting thread

Both must match the application.

1. Understand the Three Important Cable Gland Dimensions

Before looking at a cable gland size chart, it helps to understand the main dimensions involved.

Cable Outside Diameter

The cable outside diameter, often abbreviated as Cable OD, is the actual external diameter of the finished cable jacket.

For example:

• Cable OD: 5.5 mm

• Cable OD: 8 mm

• Cable OD: 12.5 mm

• Cable OD: 18 mm

This measurement determines which sealing range is required.

Cable Clamping Range

The clamping range describes the minimum and maximum cable diameters that the cable gland is designed to accommodate.

For example:

Cable range: 6–12 mm

means that the gland is intended for cables with an outside diameter between approximately 6 mm and 12 mm, subject to the manufacturer's specifications and installation requirements.

This is often the most important number for cable selection.

Thread Size

The thread size refers to the part of the gland that mounts into the enclosure.

Examples include:

• M12

• M16

• M20

• M25

• M32

• PG7

• PG9

• PG13.5

• PG21

• 1/2" NPT

• 3/4" NPT

The thread size determines compatibility with the equipment mounting hole, but does not directly tell you the correct cable diameter.

2. Why M20 Does Not Mean a 20 mm Cable

This misunderstanding causes many incorrect cable gland orders.

Consider an M20 nylon cable gland.

The M20 designation normally refers to a nominal metric thread diameter of approximately 20 mm.

It does not mean:

Suitable for a 20 mm diameter cable.

Depending on the gland design, an M20 model may be available with a cable clamping range such as:

• 5–10 mm

• 6–12 mm

• 8–13 mm

• 10–14 mm

Exact ranges vary between manufacturers and product series.

This is why simply telling a supplier:

“I need 1,000 pcs of M20 nylon cable glands”

may not provide enough information.

A better request would be:

M20 × 1.5 nylon cable gland for a cable OD of 9.5 mm.

This allows the supplier to check both the mounting thread and cable sealing range.

3. Measure the Actual Cable Outside Diameter

Always start cable gland sizing with the actual cable.

Do not select the gland based only on:

• Conductor size

• Wire gauge

• Number of cores

• Cable current rating

• AWG

• Cable cross-sectional area

For example, two 4 mm² cables may have very different outside diameters because they use different:

• Jacket materials

• Insulation thicknesses

• Shielding structures

• Number of conductors

• Armor

• Manufacturing designs

The cable gland only “sees” the outside of the cable.

Therefore, Cable OD is the critical measurement.

How to Measure Cable Diameter

For a round cable, measure across the finished outer jacket using a suitable measuring tool such as a caliper.

Measure the cable at several points if necessary.

Do not compress a soft cable jacket excessively during measurement because this can produce an inaccurate diameter.

For example:

Measured positions:

• 9.7 mm

• 9.9 mm

• 9.8 mm

The actual working diameter can reasonably be treated as approximately 9.8 mm.

You would then select a cable gland whose clamping range comfortably contains this value.

4. Consider Cable Diameter Tolerance

Production cables do not always have exactly the same outside diameter.

A cable specification might state:

Nominal OD: 10 mm ± 0.5 mm

This means actual production cables could potentially measure between:

9.5 mm and 10.5 mm

If you choose a cable gland with a clamping range of 6–10 mm, part of the cable production may exceed the recommended range.

A better gland might have a range such as:

7–12 mm

assuming all other requirements are suitable.

This is particularly important for manufacturers purchasing cable glands for mass production.

The gland must work reliably not only with a prototype cable but also with normal cable manufacturing tolerances.

5. Avoid Selecting at the Extreme Edge of the Cable Range

Suppose your cable has an outside diameter of exactly 12 mm.

You have two possible glands:

Option A: 6–12 mm cable range
Option B: 10–14 mm cable range

Which should you choose?

There is no universal answer because seal geometry and manufacturer specifications differ, but buyers should avoid automatically selecting a gland where the cable sits exactly on the maximum or minimum boundary.

Why?

At the maximum end:

• Cable insertion may become difficult

• Seal compression may be excessive

• Tightening torque may increase

• The cable jacket may be stressed

At the minimum end:

• The sealing ring may have less effective compression

• Cable retention may be reduced

• Achieving the desired ingress protection may become more sensitive to installation

Where possible, the cable OD should sit reasonably inside the gland's working range.

6. How to Read a Nylon Cable Gland Size Chart

A typical nylon cable gland size chart may contain columns such as:

For selection purposes, you should pay particular attention to:

Thread size + cable range + thread length

These three values answer three different questions.

Thread Size

Will the gland fit the enclosure?

Cable Range

Will the gland properly grip and seal the cable?

Thread Length

Is the threaded section long enough for the enclosure wall?

A correct cable range with an incorrect thread length can still create installation problems.

7. Example Nylon Cable Gland Selection Logic

The following table is intended to illustrate the selection process rather than serve as a universal product specification.

The exact cable range for each thread size varies significantly between manufacturers.

For this reason, never treat this type of table as a universal size conversion chart.

Always verify the supplier's actual technical data.

8. How to Select a Metric Nylon Cable Gland

Metric nylon cable glands are among the most widely used types in electrical and industrial equipment.

Common metric sizes include:

• M12

• M16

• M18

• M20

• M22

• M25

• M27

• M32

• M36

• M40

• M50

• M63

A metric specification may be written as:

M20 × 1.5

Here:

• M20 indicates the nominal thread diameter

• 1.5 indicates the thread pitch in millimeters

When selecting a metric nylon cable gland, confirm:

1. Cable outside diameter

2. Required cable clamping range

3. Metric thread size

4. Thread pitch

5. Thread length

6. Panel thickness

7. Environmental protection requirement

Do not assume every M20 gland has exactly the same dimensions.

9. How to Select PG Nylon Cable Glands

PG cable glands are still widely used in industrial machinery, electrical equipment, and legacy systems.

Common PG sizes include:

• PG7

• PG9

• PG11

• PG13.5

• PG16

• PG19

• PG21

• PG25

• PG29

• PG36

• PG42

• PG48

One important point is that PG numbers do not directly correspond to cable diameter.

For example, a PG13.5 gland does not mean it fits a 13.5 mm cable.

The PG designation refers to the thread standard.

A buyer replacing an existing gland should therefore check:

• Existing equipment thread

• Cable OD

• Required sealing range

If the original machine drawing says PG13.5, replacing it with an apparently similar metric gland without checking the mounting hole can create thread incompatibility.

10. Metric vs PG Cable Gland Size: Do Not Convert by Appearance

Metric and PG glands can sometimes appear similar in physical size.

For example, buyers may compare:

• M16 and PG9

• M20 and PG13.5

• M25 and PG16

However, visually similar dimensions do not mean the threads are interchangeable.

Differences may include:

• Thread diameter

• Thread pitch

• Thread profile

For new equipment designs, it is usually better to establish one thread standard and maintain consistency across the machine or product series.

For replacement applications, follow the existing equipment specification.

11. How NPT Cable Gland Sizing Is Different

NPT is commonly used in North American industrial equipment.

Typical sizes include:

• 1/4" NPT

• 3/8" NPT

• 1/2" NPT

• 3/4" NPT

• 1" NPT

• 1-1/4" NPT

• 1-1/2" NPT

Unlike common metric cable gland threads, NPT is a tapered thread system.

The size designation can also be confusing because a 1/2" NPT thread does not simply measure 0.5 inch across the outer thread diameter.

Therefore, buyers should not try to determine NPT compatibility using only a ruler and nominal size.

If the equipment drawing specifies NPT, use the specified NPT cable gland.

12. How to Match Cable Diameter and Gland Size Step by Step

Here is a practical selection process.

Step 1: Measure Cable OD

Example:

Cable OD = 8.6 mm

Step 2: Identify the Enclosure Thread

Example:

Enclosure = M20 × 1.5

Step 3: Find M20 Glands With a Suitable Cable Range

Possible supplier options might include:

• M20 / 5–9 mm

• M20 / 6–12 mm

• M20 / 10–14 mm

For an 8.6 mm cable, both the first and second options may appear possible.

Step 4: Consider Cable Tolerance

Suppose the cable can vary between:

8.3–8.9 mm

A 6–12 mm range may provide more installation allowance than a version whose upper limit is close to 9 mm.

Step 5: Check Environmental Requirements

If used outdoors, also confirm:

• IP rating

• UV resistance

• Operating temperature

Step 6: Check Thread Length

If the enclosure wall is unusually thick, verify that the standard thread is long enough.

Step 7: Confirm Before Production

For large-volume equipment production, testing samples with the actual cable and enclosure is a good practice before finalizing the complete order.

13. What Happens If the Cable Gland Is Too Large?

A gland is effectively “too large” for the cable when the cable diameter is below the gland's recommended sealing range.

For example:

Cable OD: 5 mm
Gland cable range: 8–12 mm

This combination is not suitable.

Potential problems include:

• Insufficient seal compression

• Poor cable retention

• Reduced strain relief

• Cable movement

• Dust ingress

• Water leakage

• Failure to achieve intended IP performance

Tightening the gland more aggressively is not a correct solution.

A gland designed for the correct cable range should be selected instead.

14. What Happens If the Cable Gland Is Too Small?

Now consider:

Cable OD: 13 mm
Gland cable range: 6–12 mm

Possible issues include:

• Cable cannot pass through the seal

• Excessive installation force

• Seal deformation

• Cable jacket compression

• Difficulty tightening the cap

• Damage to the internal sealing component

Do not modify the sealing ring by cutting or drilling unless the gland is specifically designed for such modification.

Use the correct size.

15. Cable Diameter Is Not the Same as Mounting Hole Diameter

Another common sourcing mistake is confusing these two measurements.

Suppose a buyer tells the supplier:

“My hole size is 20 mm.”

This information alone is not sufficient.

A 20 mm mounting hole tells you something about the enclosure, but not the cable.

The supplier still needs the cable outside diameter.

Likewise:

“My cable is 10 mm.”

also does not tell the supplier which thread is required.

The ideal RFQ contains both.

For example:

Cable OD: 10 mm
Thread: M20 × 1.5
Panel thickness: 2 mm
Application: Outdoor control box
Requirement: Waterproof / high ingress protection

This greatly reduces the risk of incorrect product selection.

16. Cable Gland Sizing for Control Panels

Control panels often use many cable sizes in the same enclosure.

For example:

• Sensor cable

• Ethernet cable

• Signal cable

• Control cable

• Motor cable

• Power cable

Trying to use one gland size for every cable is not always practical.

Instead, panel designers should create a cable entry schedule containing:

This approach improves standardization during assembly and simplifies purchasing.

17. Cable Gland Sizing for Industrial Machinery

Machinery introduces additional requirements beyond diameter.

The cable may experience:

• Vibration

• Movement

• Pulling force

• Oil exposure

• Temperature changes

• Repeated bending

Correct size remains essential, but strain relief also becomes important.

For moving cables, consider whether a standard gland is sufficient or whether a spiral strain-relief cable gland is more appropriate.

The cable clamping range still needs to match the actual OD regardless of gland structure.

18. Cable Gland Sizing for Outdoor Equipment

Outdoor cable glands should be selected based on both size and environment.

For example:

Cable OD: 11 mm
Thread: M25
Installation: Outdoor telecommunications cabinet

The selection process should include:

• Suitable M25 cable range

• Required IP rating

• UV-resistant material

• Outdoor operating temperature

• Sealing washer

• Long-term weather exposure

Choosing the correct diameter range but ignoring UV resistance can still lead to premature failure.

19. Standard Thread vs Long Thread Nylon Cable Glands

After determining the thread diameter and cable range, check the thickness of the mounting wall.

If the enclosure uses thin sheet metal, a standard thread may be sufficient.

For thicker mounting surfaces, a long-thread gland may be necessary.

Long-thread versions may be useful for:

• Thick plastic enclosures

• Cast housings

• Multi-layer panels

• Special machinery structures

Before purchasing, compare:

Available thread length vs actual mounting thickness.

A correctly sized cable seal cannot compensate for insufficient mounting thread engagement.

20. Multiple-Hole Cable Glands Require Different Sizing Logic

Some applications route multiple wires through one gland.

A multi-hole cable gland may contain a sealing insert with:

• 2 holes

• 3 holes

• 4 holes

• 6 holes

• More customized openings

In this case, selection must consider the diameter of each individual wire or cable.

For example:

Main gland thread: M25
Seal: 4 holes
Individual cable OD: 4 mm

The buyer should specify all three parameters.

Do not simply request “M25 multi-hole cable gland.”

21. Flat Cables and Special Cable Shapes

Most standard cable gland clamping ranges are intended for round cables.

If the cable is:

• Flat

• Oval

• Ribbon-shaped

• Multi-core bundle without a common outer jacket

a standard round sealing ring may not provide reliable sealing.

For special cable geometry, consult the supplier before selecting a normal gland from a standard diameter chart.

The correct solution may require a special sealing insert or custom cable entry component.

22. Why Cable Gland Size Affects IP Performance

Achieving reliable environmental sealing depends heavily on the relationship between the cable and the sealing ring.

When the compression nut is tightened, the seal must compress uniformly around the cable.

If the cable is far too small:

The seal cannot close correctly.

If the cable is too large:

The seal may become overstressed or difficult to compress correctly.

Correct diameter matching allows the sealing element to operate within its intended mechanical range.

Therefore, when an application requires an IP68 nylon cable gland, selecting the correct cable range is just as important as selecting a product labeled with the desired protection level.

23. Common Cable Gland Size Selection Mistakes

Mistake 1: “I Need an M20 Gland for a 20 mm Cable”

M20 refers to the mounting thread, not the cable size.

Mistake 2: Selecting Only From the Enclosure Hole

The mounting hole and cable diameter must both be considered.

Mistake 3: Selecting Only From Cable Diameter

Even if the cable fits the seal, the gland still needs the correct enclosure thread.

Mistake 4: Ignoring Cable Tolerance

A gland suitable for one sample cable may not work correctly across mass-production cable variations.

Mistake 5: Choosing the Cheapest Gland With the Same Thread

Two M20 glands may have different:

• Cable ranges

• Thread lengths

• Sealing structures

• Nylon materials

• Temperature ratings

They should not automatically be treated as equivalent.

Mistake 6: Mixing PG and Metric Threads

Similar-looking gland sizes do not guarantee thread compatibility.

Mistake 7: Assuming a Larger Cable Range Is Always Better

A very wide or oversized range is not automatically an advantage.

The gland must seal your actual cable reliably.

24. Information to Provide When Requesting a Quote

If you want a supplier to recommend the correct nylon cable gland size, provide the following information:

Essential Information

• Cable outside diameter

• Thread standard

• Thread size

• Required quantity

Recommended Additional Information

• Indoor or outdoor application

• Required IP level

• Minimum operating temperature

• Maximum operating temperature

• Panel thickness

• Standard or long thread

• Standard or spiral strain relief

• Nylon color

• Flame-retardant requirement

• UV resistance requirement

• Locknut requirement

• Washer requirement

A useful RFQ could look like this:

Cable OD: 9.5 mm
Thread: M20 × 1.5
Installation: Outdoor electrical enclosure
Panel thickness: 2 mm
Protection requirement: IP68
Color: Black
Quantity: 5,000 pcs

This is significantly more useful than simply saying:

Please quote M20 cable glands.

25. Quick Nylon Cable Gland Selection Checklist

Before placing an order, confirm the following:

Cable

• What is the actual cable OD?

• What is the minimum OD?

• What is the maximum OD?

• Is the cable round?

Gland

• Does the clamping range fully cover the cable?

• Is the cable too close to the minimum or maximum limit?

• Is adequate strain relief provided?

Mounting

• Metric, PG, NPT or another thread?

• What thread size?

• What thread pitch?

• What mounting hole?

• What panel thickness?

• Is a long thread required?

Environment

• Indoor or outdoor?

• Required IP rating?

• UV exposure?

• High or low temperature?

• Oils or chemicals?

• Vibration?

• Cable movement?

If all four groups are confirmed, the risk of selecting the wrong gland is greatly reduced.

Frequently Asked Questions About Nylon Cable Gland Sizes

How do I know what nylon cable gland size I need?

First determine the cable outside diameter, then identify the thread specification of the enclosure. Choose a gland whose clamping range includes the actual cable OD and whose mounting thread matches the equipment.

What size cable fits an M20 cable gland?

There is no single universal cable diameter for all M20 cable glands. The acceptable cable range depends on the gland design and manufacturer. Always check the specified clamping range.

Does M20 mean a 20 mm cable?

No. M20 refers to the metric mounting thread specification. The correct cable size is determined by the cable clamping range.

Can one M20 gland have different cable ranges?

Yes. Different M20 models may be designed for different cable diameter ranges. This allows the same enclosure thread to accommodate different cables.

Should cable diameter be in the middle of the gland range?

It does not necessarily have to be exactly in the middle, but avoiding the extreme minimum or maximum limits can provide additional tolerance when practical.

Can I use an M20 gland instead of PG13.5?

Not automatically. Metric and PG are different thread systems. Confirm the enclosure thread before replacing one standard with another.

What happens if the cable is smaller than the gland's minimum diameter?

The sealing insert may not compress adequately, potentially reducing cable retention and environmental sealing performance.

What happens if the cable is larger than the maximum range?

The cable may be difficult to insert, and the seal may be excessively compressed or damaged. Select a larger cable range instead.

How do I measure the cable for a cable gland?

Measure across the finished outer jacket of the cable using an appropriate measuring tool such as a caliper. Do not use conductor diameter or nominal conductor size as a substitute.

Do I need to consider cable diameter tolerance?

Yes, especially for production equipment. The gland should accommodate the expected minimum and maximum outside diameters of the cable.

How do I choose a cable gland for an unthreaded panel hole?

Select the appropriate gland based on the cable OD and required mounting size, then secure it through the panel using a compatible locknut where applicable.

Is thread size more important than cable range?

Both are necessary. The thread determines whether the gland fits the enclosure, while the clamping range determines whether it fits and seals the cable correctly.

Final Thoughts: Match the Cable First, Then Confirm the Thread

The easiest way to avoid cable gland sizing mistakes is to stop thinking of a gland size as one single number.

A correct nylon cable gland size is really a combination of:

Cable outside diameter + clamping range + mounting thread + thread length + environmental requirement.

For example, “M20” alone is not a complete cable gland specification.

A much more useful specification is:

M20 × 1.5, suitable for a 9–12 mm cable, required for an outdoor IP-rated enclosure.

This approach makes it easier to compare products, communicate with suppliers, prevent installation problems, and maintain consistent sealing performance across production batches.

Before purchasing, always measure the actual cable, verify its dimensional tolerance, confirm the enclosure thread, and check that the cable sits comfortably within the gland's specified clamping range.

For manufacturers, electrical panel builders, equipment companies, distributors, and project buyers sourcing Nylon Cable Glands, YDT can support cable gland selection based on your actual cable OD, thread standard, mounting requirements, application environment, and purchasing quantity. Send us your cable diameter, Metric/PG/NPT thread specification, required IP rating, and application details, and YDT can help you match the appropriate nylon cable gland size for your project.