Large Metric to NPT Thread Adapters — Machined to Order

Need to put a metric cable gland into an NPT enclosure hub — or an NPT conduit fitting into a metric knockout — at M50, M63, M75, M90 or M100, and the catalogs stop at small brass sizes? We machine the large conversion adapter to order: male or female either end, 304/316 stainless or nickel-plated brass, O-ring sealed. From a sketch, no CAD, one piece up. Get a quote →

Where the catalogs stop, the lathe starts

Small metric-to-NPT adapters exist as stock items — nickel-plated brass, mostly, and mostly below M63. Go bigger and the choices collapse: M75, M90 and M100 conversions in 316 stainless are not warehouse items, specific male/female orientations are missing, and non-nearest size jumps (an M63 gland into a 3" hub) exist in no catalog at all. American enclosures, NEMA boxes and hazardous-location housings are threaded NPT; European and Asian glands and equipment entries are metric. On large industrial cabinets, packaged skids and machine enclosures, the two systems meet constantly — and at these diameters the adapter is turned from large bar stock in low volume. That is machining work, and it's exactly what we do.

Size crossover & weight table

The dimensionally nearest metric/NPT pairs, with the approximate weight of a typical adapter in 304 stainless — so you know what you're shipping before you ask:

Metric end	Nearest NPT	NPT thread OD	Approx. weight (304)
M50×1.5	1½" NPT	48.3 mm	≈ 0.9 kg
M63×1.5	2" NPT	60.3 mm	≈ 1.5 kg
M75×1.5	2½" NPT	73.0 mm	≈ 2.2 kg
M90×2	3" NPT	88.9 mm	≈ 3.2 kg
M100×2	3½" NPT	101.6 mm	≈ 4.0 kg

Weights vary with length, bore and form — the exact figure goes on your drawing before you order. Non-nearest combinations are just as machinable: M63 male to 1½" NPT female, M75 to 3", M90 to 4", or BSP/G threads instead of NPT on either end. In 6061 aluminum the same parts weigh roughly a third of the stainless figures above.

Taper meets parallel: how each end seals

This conversion joins two different sealing philosophies, and a good adapter respects both:

Forms & options

Option	Choices	Notes
Direction	Metric male → NPT female · NPT male → metric female	Either way, any pairing
Form	Adaptor (same size class) · reducer · enlarger · male-male nipple	Per CMP/gland-industry naming
Threads	M50–M100+ (EN 60423 gland sizes) · 1½"–4" NPT · BSP/G on request	Both ends gauged
Seal	O-ring shoulder groove · flat gasket face · plain	Keeps the enclosure IP rating
Material	304 stainless steel · 316 stainless · nickel-plated brass · 6061 aluminum	316 for offshore & washdown
Bore	Full through-bore for cable bundles or conduit fill	Sized to your cable OD
Body	Hex or octagonal wrench flats · knurled grip ring	Flats sized to standard wrenches

Where they're used

• Imported machinery on US sites — European cabinets arrive with metric knockouts; site conduit and fittings are NPT. One adapter per entry instead of re-punching panels.
• US enclosures with European glands — NEMA and hazardous-location boxes are NPT; the specified EMC or Ex cable glands are metric.
• Packaged skids & generator sets — large cable bundles entering through M75–M100 glands into NPT-threaded junction hubs.
• Marine & offshore cabinets — 316 stainless conversions that don't gall or streak rust where plated brass fails.
• Pump, valve & instrument housings — large conduit entries adapted to the housing's native thread without modifying a certified casting.

Related adapters we machine

Where the Catalogue Stops for This Size Pair

Large metric to NPT is where stock ranges end — the sizes get big and the combinations multiply.

What you need	In the catalogue?	How we machine it
A plain coarse-to-coarse reducer in this size step	Sometimes stocked	If a stockist lists it, buy it off the shelf. We are worth calling when the pitch, length, material or form is not on their page.
A large metric port against an NPT line	No	US equipment into a large ISO metric port, or the reverse. Both ends cut on one bar.
Different pitch on each end	No	Each thread single-pointed to its own pitch on the same bar.
Double-male stud instead of a bush	Thin	Male on both ends; far fewer sizes stocked and almost none in mixed pitch.
Female-female coupling	Thin	Joins two studs rather than reducing a hole. Any pitch pair.
Hex flats sized to a spanner you already own	No	Cut to your wrench, not to a catalogue table.
Through-bore for a shaft, cable or fluid	No	Bore and both threads cut in one setup so they stay concentric.
Shortened body for a crowded plate	No	Catalogue parts come in one length. State the space you have.
Left-hand thread on either end	No	Not stocked at any size.
316 stainless or alloy steel instead of plated mild steel	Rare	Material is open; no tooling cost at these sizes.

See also the fitting thread identification chart and valve fittings for metric valve ports on NPT lines.

Frequently asked

Which NPT size matches my metric cable-gland thread?

Nearest pairs: M50 ↔ 1½", M63 ↔ 2", M75 ↔ 2½", M90 ↔ 3", M100 ↔ 3½". Because every adapter is machined to order, non-nearest jumps (M63 → 1½", M90 → 4") are cut the same way when that's what your hardware actually is.

NPT is tapered and metric is parallel — how does the joint seal?

Each end by its own rule: the NPT taper seals metal-on-metal with sealant or tape; the parallel metric end seals on an O-ring or gasket at the shoulder, like any IP-rated gland. We machine both features to their standards (ASME B1.20.1 and EN 60423).

Why can't I buy a large metric-to-NPT adapter off the shelf?

Stock metric-to-NPT adapters are mostly small nickel-plated brass. Large sizes in 316, specific orientations and non-nearest combinations aren't stocked — at M75+ the part is turned from large bar in low volume. More on joining two different threads →

How heavy are these adapters and what materials do you machine?

Roughly 0.9 kg (M50/1½") up to 4 kg (M100/3½") in 304 stainless — exact weight stated on your drawing before you commit. 304 or 316 stainless steel, nickel-plated brass, or 6061 aluminum at about a third of the weight. MOQ one piece, no CAD needed.