A 1/2 in trade size cord grip connector takes a 0.875 in (7/8 in, 22 mm) hole; a 1 in fitting takes 1.375 in (1-3/8 in, 35 mm). Put the threaded head on the outside face with its sealing washer under it, and run the locknut up from the inside until it bottoms on the wall. Our stainless enclosures are rated NEMA 4X / IP66 by the manufacturer; not UL listed. The fitting you drop into that hole carries its own rating, and the finished assembly keeps only the weaker of the two. Drill with a step bit at about 175 RPM in stainless, deburr both edges, and the box is sealed again the same shift.
Hole size by trade size
The hole follows the fitting's screw threads, and the trade size names them. It says nothing about the cord: the seal grips the range of jacket diameters printed on the fitting body or its datasheet. US literature calls this same part a strain relief or cord connector; the cable gland vs cord grip article sorts out the naming across specifications. The cutouts, glands and windows guide covers fitting types and window openings in depth; this page sticks to the number you drill.
UL 50 Table 71-1A sets the nominal knockout diameter for each trade size, and these are the holes the fittings thread into:
| Fitting trade size | Hole diameter | Metric | What it usually carries |
|---|---|---|---|
| 3/8 in | 0.625 in (5/8 in) | 15.9 mm | small hubs and signal cords |
| 1/2 in | 0.875 in (7/8 in) | 22.2 mm | one power cord; the everyday choice |
| 3/4 in | 1.109 in | 28.2 mm | thicker jackets or a multi-cord seal |
| 1 in | 1.375 in (1-3/8 in) | 34.9 mm | large jackets or several cords in one seal |
| 1-1/4 in | 1.734 in | 44.0 mm | large multi-cord seals and hubs |
| 1-1/2 in | 1.984 in | 50.4 mm | conduit hubs |
| 2 in | 2.469 in | 62.7 mm | big conduit or multi-gland plates |
A single ten-step bit, in steps of 1/8 in, covers the whole table, and its two largest steps land exactly on their trade sizes. The 3/4 in size falls between steps: 1-1/8 in (1.125 in) is 0.016 in over its 1.109 in knockout, and that much seals when the head washer overhangs the hole all the way round. Judge the washer, not only the number. Metric-threaded glands (M12, M16, M20, M25) cut to their own hole series; the M20 hole size article lists those.
What you need
- A cord grip picked for the cord: read the printed clamping range on the body and keep the round jacket inside it.
- Its locknut and sealing washer; plastic fittings supply plastic locknuts, metal fittings take metal ones.
- A step drill bit from 1/4 in to 1-3/8 in, HSS or cobalt, or a hole saw above that.
- A drill that holds low speed: the 7/8 in step wants about 175 RPM in stainless.
- Cutting oil, a center punch and a deburring tool.
- A dead-tested supply: unplug the cord and verify the wall is de-energized before the first chip, because what passes through these fittings is usually mains power.
Cutting the hole
- Pick the fitting from the cord, then read the hole from the table. A 0.35 in [9 mm] jacket, the kind on a de-icer cord, wants a fitting whose printed range lists it, not merely a 1/2 in hole.
- Mark the hole on the outside face and center-punch it. Keep the edge at least 1/2 in (12 mm) from any bend, seam or weld so the washer lands on flat metal.
- Clear at least 1 in (25 mm) behind the wall for the locknut and the cord, and pull the backplate back if it sits closer.
- Start on the punch mark with cutting oil, and size the speed to the largest step in the cut. For HSS in 304 or 316L, cutting at 30-50 SFM: RPM = SFM × 12 / (π × D in). On the 7/8 in step at 40 SFM, that is 40 × 12 / (3.1416 × 0.875) = 480 / 2.75 = 175 RPM. The same step runs about 131 RPM at 30 SFM and 218 RPM at 50 SFM. Feed firmly so the bit cuts instead of rubbing the surface hard; bit choice and feeds for 304 are in the stainless drill-bit guide.
- Deburr both faces and put a light chamfer on the outside edge so the washer seats flat. Above the bit's largest step, a hole saw does the work; the stainless cutting article covers saw speeds and layout.
Fitting the cord grip
- Take the fitting apart and slide the parts onto the cord in the order they came off, dome cap outermost and clamp insert next, so the clamp lands on the round jacket, never on the conductors.
- Pass the threaded neck through the hole from the outside so the head and its washer sit flat on the outer face.
- Run the locknut on from the inside: hand-tight, then a quarter to half a turn with pliers until it bottoms. The neck threads should show fully through the nut.
- Tighten the dome cap hand-tight plus about half a turn, until the clamp insert just dimples the jacket.
- Pull the cord hard by hand; the jacket must hold and the fitting must not rock.
A molded plug never passes through a cord grip; the clamp grips bare jacket only. Pass the cord and terminate inside, or see the molded plug through a knockout article for the workarounds.
Checks when done
- The washer is compressed evenly all round, with no daylight under the head.
- The locknut is bottomed and the fitting does not rock or turn by hand.
- The clamp has dimpled the jacket, and the cord does not slide under a firm pull.
- No swarf is left inside; a loose chip cuts a gasket or shorts a terminal.
- On a rated box, the fitting's printed rating matches or beats the box rating, because the assembly keeps the weaker of the two.
Mistakes that cost the rating
- Snap-in clamp connectors sold for NM cable are dry-location, indoor parts. On a washdown box they drop the assembly to their own rating, which is usually no Type 4 at all; a threaded cord grip with a sealing washer is the part that keeps it. The fittings article for Type 4X drive enclosures lists what to look for.
- An oversize or oval hole leaves the washer sitting on air. One trade size up is recoverable with a washer that still overhangs flat metal; beyond that, the wrongly-drilled-hole article has the sealing options.
- The head mounted inside puts the gasket on the dry side, and the exposed thread wicks water straight in. Head outside, every time.
- A plastic locknut under a metal body loosens with temperature swings; match the locknut to the body.
- A field-cut hole in a listed panel raises a listing question of its own; the knockout-and-listing article covers when that matters.
When to order the holes cut
For a one-off repair, drill it yourself; for production panels, or a wall with three or more entries, order the cutouts with the box. The cutout designer lays out holes, glands and operators on any face of a catalog or custom size, checks the spacing and exports the layout with your quote request. Edges arrive deburred and flat, so every washer seats the same, and the box is delivered in 10 business days anywhere in the world; for custom work the count starts at your approval of the drawing. When the standard wall is too crowded for the entries a job needs, the custom stainless page compares a standard body with new openings against a fully custom one.
Catalog dimensions to compare
Compare these catalog dimensions with your component layout. Open each enclosure for its rating, material and usable space, then check those specifications against your application.
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 12 × 10 × 6 in | 304 stainless | 12 x 10 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 16 × 14 × 8 in | 304 stainless | 16 x 14 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 20 × 16 × 8 in | 304 stainless | 20 x 16 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Does the cord grip head go inside or outside the wall?
Outside. The sealing washer under the head presses against the outside face, where the water runs; water tracking down the cord meets the gasket first. Mounted inside, the gasket sits on the dry side and the exposed thread wicks water straight into the box. Head outside, gasket outside, locknut inside at a quarter to half a turn past hand-tight, and leave a drip loop in the cord below the fitting so runoff drops off before it reaches the head.
Will a snap-in cord grip keep a NEMA 4X box sealed?
Only when the fitting itself carries the rating. Look for the marking on the body or its datasheet: Type 4X or IP66 for a washdown box, and treat any part marked only for NM cable as a dry-location fitting. The weakest part sets the assembly rating, so one dry-only snap-in drags a manufacturer-rated Type 4X / IP66 box down to that fitting's rating.
What cord size fits a 1/2 inch cord grip connector?
Trade size names the thread, not the cord. Read the clamping range printed on the fitting and keep the round jacket inside it; for example, a range marked 0.16-0.43 in [4-11 mm] seals a 0.35 in [9 mm] de-icer cord with margin at both ends. A jacket at the edge of the range, or bare conductors under the clamp, leaks and gives no strain relief.
The hole came out oversized. Can I still seal the fitting?
Sometimes. Up to about 1/16 in of oversize still seals when the head washer overhangs the hole all round and sits flat on metal. Beyond that, step up one trade size using the hole table above, or fit a rated blanking plug; filler never restores the rating. The wrongly-drilled-hole article lists the remaining sealing options.
