Metric, PG, and NPT Cable Gland Threads: How to Specify the Entry

Read the enclosure drawing before choosing the gland

The gland has two different interfaces: its mounting thread connects to the enclosure, while its insert grips and seals around the cable. Identify the enclosure entry from a controlled drawing or a properly checked thread measurement. Record the complete designation, including pitch where applicable, rather than a rounded outside diameter. A gland may accept the cable perfectly yet fail to match the panel thread. For replacement work, retain the original part markings and photographs, but use dimensional confirmation before placing the order.

Understand why close diameters do not mean a match

Metric threads use metric diameter and pitch designations. PG is a separate thread system, and NPT is a tapered pipe thread with its own size and pitch conventions. LAPP's dimension tables list them separately because a nearby diameter does not establish compatibility. For example, M20 and PG13.5 should not be treated as direct substitutes merely because their outside dimensions appear similar. Forcing an incorrect thread risks damaging the entry and leaves the mounting and sealing arrangement outside its intended specification.

Resolve the mounting and seal details

State whether the gland enters a tapped hole or passes through a clearance hole with a locknut. Include panel thickness, available thread engagement, access for tightening, and any washer or sealing element required by the selected assembly. If an adapter is necessary, specify both thread interfaces and obtain confirmation of the resulting arrangement. An adapter adds dimensions and another connection that must be considered. Do not assume a thread conversion automatically preserves the original assembly's ingress protection or other declared performance.

Keep thread selection separate from cable diameter

After confirming the entry, select the insert or gland variant whose declared clamping range covers the cable's actual outside diameter. The same mounting thread can be offered with different sealing ranges, so the thread designation is not a complete order code. Add cable shape, jacket material, required strain relief, environment, and any shielding requirement to the inquiry. For DUCHUANG, supply the enclosure drawing and cable specification together, then request a fully identified gland and accessory combination for review.

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