PG threads (Panzer-Gewinde, also called steel-armour or armoured conduit thread) cannot be directly swapped for metric threads because the two systems use different flank angles, depths, and pitches [S1][S3].
PG is a straight thread with an 80° flank angle and shallow depth, while metric cable gland threads follow DIN EN 60423 with a 60° flank angle; the two are not interchangeable in the mechanical sense, only by clamping-range overlap [S5][S8].
Why PG and metric threads are not 1:1 swappable
PG thread depth is shallower than metric, but the flank angle is wider (80° vs 60°), giving PG a wider pitch on a straight thread; metric is written M + diameter × pitch (e.g. M20×1.5) under DIN EN 60423 [S3][S5]. That geometric mismatch is the root cause: even when the bore diameters look similar, the thread profile is different, so a PG-threaded gland will not seal correctly in a metric-tapped enclosure and vice versa. The product standard for cable glands is DIN EN 62444, with thread forms covered separately by ISO 965 (metric) and DIN 40430 (PG) [S4].
NPT, the third common family, adds a 1:16 taper so the flanks seal against each other on torque, which is a third mechanical pattern again and not interchangeable with either PG or metric [S3]. In practice, PG has been progressively displaced by metric in new European panel building, but it remains common in older industrial and outdoor equipment [S2][S7].
Standard cross-reference: PG to metric thread sizes
The widely used conversion pairs, taken from manufacturer and distributor tables, are: PG7 ≈ M12; PG9 ≈ M16; PG11 ≈ M16/M20; PG13.5 ≈ M20; PG16 ≈ M20/M25; PG21 ≈ M25; PG29 ≈ M32; PG36 ≈ M40; PG42 ≈ M50; PG48 ≈ M50/M63 [S2][S9][S10]. Because clamping range drives the actual fit, several PG sizes map to two metric sizes (PG11/13.5/16 all overlap M20; PG36/42/48 all overlap M50/M63), so the cable OD, not the thread code, is the deciding variable.
Numeric PG bore diameters (mm) that the conversion is anchored on: PG7 12.5, PG9 15.2, PG11 18.6, PG13.5 20.5, PG16 22.5, PG21 28.3, PG29 37, PG36 47, PG42 54, PG48 59.3 [S1][S9]. The corresponding metric outside-thread diameters are the standard M-values (M12, M16, M20, M25, M32, M40, M50, M63), and the panel hole drilled for each is typically the thread OD plus a small clearance.
Clamping range is the real selector, not the thread code
A cable gland code defines two independent things: the thread that mates to the enclosure, and the cable OD range that the rubber insert seals [S4]. Standard metal-gland ranges: M12×1.5 covers 3–6.5 mm cable, M16×1.5 covers 4–8 mm, M20×1.5 covers 6–12 mm, M25×1.5 covers 10–14 mm, M32×1.5 covers 15–22 mm, M40×1.5 covers 18–25 mm, M50×1.5 covers 32–38 mm, M63×1.5 covers 37–44 mm [S4]. On the PG side, PG11 commonly fits 5–10 mm cable OD as a working range [S4].
Selection rule of thumb: pick the gland where your measured cable OD lands near the middle of the clamping range, then choose the thread family to match the existing enclosure hole [S4][S6]. If the enclosure is already drilled for PG, do not retap to metric as a thoughtless upgrade; verify the thread profile, panel thickness, and any locknut/EMC back-shell compatibility first. For reference, the cable gland encyclopedia entry covers thread-form geometry, IP ratings, and material options in more depth, and a broader cable and wire overview places gland sizing inside the wider conductor-and-OD selection problem.
Decision matrix: PG, metric, and NPT on six criteria
Thread family comparison for typical industrial panel builds: (1) Standard: PG is DIN 40430, metric is DIN EN 60423 / ISO 965, NPT is ANSI/ASME B1.20.1 [S4][S5]. (2) Flank angle: PG 80°, metric 60°, NPT 60° with 1:16 taper [S3][S8]. (3) Sealing mechanism: PG and metric seal on the rubber insert and an O-ring under the face; NPT seals on thread flanks plus sealant [S3]. (4) New-build preference in Europe: metric dominant, PG legacy, NPT mostly for North American equipment and process piping entries [S2][S7]. (5) Spanner/hex size: each family has its own across-flats dimension; the same nominal bore does not share a hex across families, so PG and metric wrenches are not drop-in replacements [S10]. (6) Conversion risk: medium for PG↔metric (geometry mismatch, often clamped-range-only safe), high for either with NPT (tapered vs straight, different sealing).
For new European control cabinets and machine builds, specify metric (DIN EN 60423) glands and match to a control cable or power cable OD. For retrofit on existing PG-tapped panels, keep PG and do not assume a like-numbered metric gland is a drop-in; the 80° flank and the 60° flank do not mate. For North American process skids and any threaded conduit entry, NPT remains the default and should be paired with thread sealant rated for the cable jacket material.
Failure modes and limits of cross-reference tables
Three common pitfalls when using a PG-to-metric table. First, two PG sizes mapping to the same metric size (e.g. PG13.5 and PG16 both to M20) means the metric gland is not a unique replacement; the cable OD range and the hex/spanner size of the existing nut still differ, so locknut and EMC back-shell parts may not reuse [S2][S10]. Second, the same "size code" does not guarantee the same cable OD range; an M20 in one maker's catalog can be 6–12 mm while a competitor's M20 wide-range insert is 8–17 mm, and a PG11 in the same maker is 5–10 mm [S4][S6]. Third, IP rating drift: mixing a metric gland with a PG locknut, or vice versa, can drop the joint below IP68 because the face seal and the O-ring land are not co-designed.
What the tables explicitly do not do: they do not convert a PG bore diameter into a metric thread by calculation; the values listed are clamping-range-based cross-references, not geometric conversions [S1][S2]. For exact thread engagement, the controlling documents are DIN 40430 (PG) and DIN EN 60423 (metric) on the gland side, and the enclosure's own drilling/tapping drawing on the panel side [S4][S5].
Sourcing, standards, and the trend in 2026
PG cable glands are still widely available from European stockists and remain common on older industrial equipment, but they are increasingly relegated to "exceptional cases" and replacement-only use, with metric specified on new builds [S2]. The product-level safety and performance standard is DIN EN 62444, covering cable glands for electrical installations; thread-form standards are ISO 965 (metric) and DIN 40430 (PG) [S4][S5]. Common protection ratings on stocked glands are IP68 and IP69K, with EMC-gland variants specified where drive or instrument cable runs need 360° shield termination [S5].
For gland packing and sealing insert selection in chemical or offshore service, treat the thread-family question as separate from the material question: a metric M20 in PA66 nylon, brass, or SS316L all carry the same M20×1.5 thread, so the family choice (PG vs metric) and the material choice (PA vs brass vs 316L) are independent decisions and can be specified in the same line item.
Trackable signals for the rest of 2026: continued shrinkage of PG-only distributor stock in favour of metric, more PG-to-metric adapter glands (one side PG male, other side metric female) for retrofit on existing enclosures, and tighter IEC 62444 enforcement on declared clamping ranges versus actual lot-tested ranges.
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