Although the difference between M16 and M20 appears to be only 4 mm in nominal thread diameter, the choice affects enclosure hole dimensions, installation space, and the range of cable diameters that can be accommodated. Selecting the correct size requires checking both the enclosure entry and the cable's actual outside diameter rather than relying on the thread designation alone.
What Is the Difference Between M16 and M20 Cable Glands?
The main difference is the nominal diameter of the external metric thread. An M16 cable gland has a nominal thread diameter of 16 mm, while an M20 cable gland has a nominal thread diameter of 20 mm. Both are commonly available with a 1.5 mm thread pitch, although the exact specification should be confirmed from the product drawing.
The larger M20 thread generally requires a larger enclosure entry and may be offered with a cable clamping range suitable for thicker cables. However, a larger thread does not automatically mean that every M20 gland accepts a larger cable than every M16 gland. Different gland designs can have overlapping cable ranges.
|
Comparison Item |
M16 Cable Gland |
M20 Cable Gland |
|---|---|---|
|
Nominal external thread diameter |
16 mm |
20 mm |
|
Typical metric thread |
M16 × 1.5 |
M20 × 1.5 |
|
Example cable diameter range |
Approximately 4–10 mm |
Approximately 6–13 mm |
|
Enclosure entry |
Smaller opening |
Larger opening |
|
Common selection consideration |
Compact cable entries and smaller cables |
Larger cable entries and cables requiring a wider clamping range |
|
Key specification to verify |
Thread, cable range, sealing structure |
Thread, cable range, sealing structure |
The cable ranges in this table are indicative examples for general-purpose cable glands, not universal specifications. Actual limits vary by manufacturer, material, sealing insert, and product series.
How Do M16 and M20 Thread Sizes Affect Installation?
Thread size determines how the cable gland attaches to the enclosure. Before installation, confirm whether the enclosure has a pre-threaded entry or a plain clearance hole that requires a locknut.
An M16 gland is suitable when the enclosure design provides a compatible M16 entry. Its smaller threaded section can help reduce the space occupied by individual cable entries, which may be useful in compact control boxes or equipment with multiple low-diameter cables.
The installer should verify the required hole diameter, thread pitch, usable thread length, and enclosure wall thickness. If a locknut is used, sufficient clearance must also be available on the inside of the enclosure.
An M20 gland requires a larger compatible entry. It may be preferable when the cable has a larger outside diameter or when the selected gland series provides a suitable clamping range in this size.
However, replacing an M16 gland with an M20 gland is not simply a matter of choosing a larger fitting. The enclosure opening must accommodate the M20 thread, and the surrounding space must allow the gland body, sealing nut, and installation tools to fit. If the enclosure is already manufactured, the existing entry size may limit the available choices.
Important: M16 and M20 glands are not directly interchangeable because their external threads have different nominal diameters.
What Cable Diameter Can M16 and M20 Cable Glands Accommodate?
The accepted cable diameter is one of the most important specifications when selecting a cable gland. Manufacturers normally state a minimum and maximum clamping diameter, measured across the cable's outer sheath.
For example, a general-purpose M16 gland may accept a cable with an outside diameter of 4–10 mm, while an M20 model may accept 6–13 mm. These figures are examples only; a particular product may use a narrower, wider, or differently positioned range.
Use a caliper to measure the cable across its outer jacket before ordering. For round cables, take measurements at several points if the jacket is flexible or slightly oval.
For multicore cables, measure the complete outer sheath rather than an individual insulated conductor. For armoured cables, follow the manufacturer's specified measurement points because the bedding diameter, armour diameter, and overall cable diameter serve different purposes during gland selection.
M16 vs. M20: Which Size Should You Choose?
The correct size depends on the cable, enclosure, installation environment, and required protection level. Neither M16 nor M20 is inherently better for every application.
The enclosure has a compatible M16 entry.
The cable's measured outside diameter falls within the selected gland's specified clamping range.
The installation requires a relatively compact cable entry.
The available mounting space and internal clearance suit the smaller gland body.
The enclosure is designed with an M20 entry or can be safely prepared for one.
The cable diameter exceeds the range of the selected M16 model but fits an available M20 variant.
The installation requires a larger threaded connection.
The gland's sealing and mechanical specifications meet the operating conditions.
A practical selection sequence is to identify the enclosure thread first, measure the cable second, and then select a gland whose clamping range covers the measurement. If the enclosure and cable requirements do not match, evaluate another gland configuration or a suitable specified adapter rather than forcing incompatible components together.
How Do Material and Protection Requirements Affect Selection?
Thread size and cable diameter are only two parts of the specification. The gland material, sealing system, and protection rating also influence whether a product is suitable for the installation.
Nylon or polyamide glands are commonly considered for general electrical installations where the cable does not require a metallic armour termination or a dedicated conductive bonding path. Their suitability depends on the material grade, operating temperature, mechanical requirements, and environmental exposure.
Metal glands may be selected where mechanical strength, environmental resistance, electrical bonding, or application-specific requirements call for a metallic construction. Nickel-plated brass and stainless steel have different properties, so material selection should consider corrosion exposure, contact requirements, and the equipment specification.
An IP rating describes protection against the ingress of solids and water under defined test conditions. The rating of a cable gland assembly depends on the product design and correct installation, including the cable diameter, sealing components, enclosure interface, and any required sealing washers.
For outdoor equipment or installations exposed to moisture and dust, confirm that the complete assembly meets the required IP rating. Do not assume that choosing an M20 gland automatically provides better protection than choosing an M16 gland.
For shielded cables, electromagnetic compatibility (EMC) may also be relevant. If the application requires shield continuity or 360-degree shield termination, select a gland specifically designed for that purpose.
Common Mistakes When Choosing M16 and M20 Cable Glands
Several selection errors can lead to installation delays, inadequate sealing, or unnecessary enclosure modifications.
|
Common Mistake |
Why It Causes Problems |
Recommended Action |
|---|---|---|
|
Selecting by thread size alone |
The cable may fall outside the gland's clamping range |
Check the exact cable diameter range on the datasheet |
|
Assuming all M20 glands accept the same cable diameter |
Different series may use different sealing inserts |
Compare the model-specific minimum and maximum diameters |
|
Ignoring the enclosure entry |
The gland may not match the existing hole or thread |
Confirm thread type, diameter, pitch, and mounting method |
|
Using an oversized gland for a thin cable |
The seal may not compress correctly |
Select a suitable clamping-range variant |
|
Overlooking environmental conditions |
Material or sealing performance may be unsuitable |
Verify IP rating, temperature range, and corrosion requirements |
|
Treating metric and other thread standards as interchangeable |
Threads may not engage or seal correctly |
Confirm whether the entry is metric, PG, NPT, or another specified type |
These checks are particularly important in repeat production. Confirming the gland specification before enclosure machining or purchasing helps avoid mismatched components across an assembly batch.
Why Choose Gordon Electric for Cable Glands?
Since 2012, Hangzhou Gordon Electric Co., Ltd. has specialized in cable glands, cable ties, flexible conduits, and electrical wiring accessories, serving international customers with in-house manufacturing and customization support.
- Manufacturing Capacity: A 6,000 m² production facility, over 20 injection molding machines, and a monthly production capacity of 150 tons support bulk orders.
- Product Customization: Metric, PG, NPT, and G thread options, along with different materials, colors, and configurations, accommodate various installation requirements.
- Quality and Compliance: CE, RoHS, REACH, UL, and other certification information supports applicable product compliance requirements.
- Export Support: Experience with international orders and access to Ningbo and Shanghai ports supports export coordination.
For M16 and M20 cable glands, customers can provide cable diameter, thread specifications, material preferences, and protection requirements to help identify suitable products.
