Short answer: the inward-key punch you are hunting is a one-off die, and the shop fix is a plain round hole plus a keyed washer. Drill the main hole at Ø16.2 mm [0.64 in], add a Ø3 mm [0.12 in] side hole 11 mm [0.43 in] away, and let the washer's bent tongue carry every twist the switch ever sees. A double-D anti-rotation ring does the same job when the switch has flats instead of a key slot, and a plain pushbutton needs nothing but its nut. The numbers below assume a 16 mm bushing switch on a stainless wall-mount box; panel thickness changes drill speeds, never the layout.
Can you buy a punch that cuts the inward key?
No — the keyway is a slot in the switch's threaded bushing, so the hole needs a tooth of panel material standing inward, and a punch that keeps material inside the cut is a custom die rather than a stock round, D or double-D tool.
A round punch shears everything inside its diameter. An inward key asks the tooling to leave one small nib standing while the rest of the disc falls out, so the die carries a nib and the punch carries a matching relief. You can build that pair yourself if you have made die sets before, and it earns its keep only at quantities where you would also mould the feature into the panel instead.
Stock tooling covers the profiles either side of it: round holes, D and double-D shapes, and keys notched on the outside edge of the hole. IEC 60947-5-1 covers control-circuit devices such as pushbuttons, and panel-mount versions come in 16 mm, 22 mm and 30 mm bushings. The 22 mm [0.87 in] size is the volume standard in industrial panels, and that is where punch tooling concentrates.
If a production run needs thousands of identical panels, price the notch die. Below that, the washer method wins on tooling cost, on lead time, and on every panel after the first.
What stops a 16 mm switch turning in a round hole?
A keyed anti-rotation washer does it: its inner key engages the bushing's slot, its bent tongue drops into a Ø3 mm [0.12 in] hole 11 mm [0.43 in] from the main hole, and switch, washer and panel become one locked chain.
The chain matters more than any single part. The bushing slot takes the washer's inner key, the washer's rim tab takes the panel, and the lock nut clamps the stack, so rotation has nowhere to go.
| Switch in the hole | Anti-rotation part | Holes to cut |
|---|---|---|
| Plain pushbutton or toggle | None — nut and gasket friction hold it | 1 × Ø16.2 mm [0.64 in] |
| Selector, key switch or E-stop with a keyed bushing | Tongue washer | Ø16.2 mm + Ø3.0 mm at 11.0 mm centers |
| Switch with a double-D boss | Double-D ring, bore over the flats | Ø16.2 mm round, plus the ring drawing's stop hole |
| E-stop with a pull-and-twist release | Tongue washer, sealant bed, nut tight | Ø16.2 mm + Ø3.0 mm at 11.0 mm centers |
The twist load is real. A 40 mm [1.6 in] mushroom head puts an annoyed thumb's push 20 mm from the axis, two and a half times the torque of the same push on a 16 mm [0.63 in] plain button at 8 mm. Rubber-washer friction copes with pushbuttons; on a small E-stop, hand the load to a steel tab.
What do you need for the washer method?
Four tools and two parts cover one switch: a Ø4 mm [0.16 in] pilot drill, a Ø16.2 mm [0.64 in] drill or reamer, a Ø3 mm [0.12 in] drill, a deburring tool, then the keyed washer plus the switch's own lock nut and gasket.
- On drill sizes for the main hole, the FAQ above carries the fractional-set arithmetic: 5/8 in reamed, 21/32 in overshot.
- The keyed washer: inner key slot for the bushing, bent tab at the rim. Match it to the bushing size and key width it lists.
- A double-D ring instead, when the switch boss has flats rather than a slot.
- Neutral-cure silicone for the sealant bed on a washdown panel; fit the washer dry on an indoor door.
- A layout template, scriber and centre punch to mark both centers before any metal moves.
Where does the tongue hole sit next to the main hole?
Drill the Ø3 mm [0.12 in] tongue hole 11.0 mm [0.43 in] center-to-center from the Ø16.2 mm hole; that spacing leaves a 1.4 mm web of panel between the two cuts, enough that drill wander never breaks through.
The sum, for a 16 mm switch on a 1.5 mm [0.06 in] stainless door or a 2 mm [0.08 in] plastic panel:
- Main hole radius: 16.2 ÷ 2 = 8.1 mm.
- Tongue hole radius: 3.0 ÷ 2 = 1.5 mm.
- Web between the cuts: 1.4 mm.
- Center distance: 8.1 + 1.5 + 1.4 = 11.0 mm [0.43 in].
- Washer size: the tab must reach 11.0 mm from the axis, so a 24 mm [0.94 in] outer diameter lands its rim tab squarely over the side hole.
What moves the 11.0 mm: a Ø3.2 mm tab hole pushes the center distance to 8.1 + 1.6 + 1.4 = 11.1 mm, and a 2 mm web gives 11.6 mm. The clock position is yours to choose, because the tab rides anywhere on the washer's rim; put the side hole where the legend needs the marked positions to read.
Mark both centers from a template; a cutout layout template keeps the pair square to the door edges. In 304 or 316L, drill speed and feed decide whether the hole runs true or work-hardens the spot, so follow the drill bit speed and feed guide for stainless. On a box you are ordering rather than drilling, the cutout designer lays out both holes, checks the spacing and sends the layout with the quote request.
How do you fit the washer and tighten the nut?
Fit the switch from the front and the washer from behind: the inner key slides over the bushing's slot, the bent tab drops into the 3 mm hole, and the lock nut goes on hand-tight plus a small-pliers nip while you hold the bezel still.
- Read the switch drawing first: keyed bushing or double-D flats, and where the slot points when the actuator sits in its marked position.
- Scribe both centers from the template, centre-punch, and drill the Ø4 mm [0.16 in] pilots.
- Open the main hole to Ø16.2 mm [0.64 in] and deburr both faces; in stainless, keep the feed up so the bit cuts rather than rubs.
- On a box that is already installed and wired, de-energize and lock it out before the Ø3 mm [0.12 in] side hole goes in; drill at 11.0 mm centers and deburr.
- On a washdown panel, lay a bead of neutral-cure silicone around both holes on the inside face; on a dry indoor door, fit the washer dry.
- Slide the washer over the bushing so the inner key engages the slot, bend the tab flat against the sheet and drop it into the side hole.
- Seat the switch's gasket under the bezel, start the lock nut and tighten it snug with small pliers while the bezel stays put; wipe the silicone squeeze-out and let it cure per its instructions.
- Prove the function: run the actuator through full travel, and on an emergency-stop latch it, twist-release it and confirm the machine stops.
Three checks tell you the job is done:
- Two fingers on the mushroom head cannot turn the switch without the washer and panel moving with it.
- The legend lines up with the marked position at every detent.
- The gasket under the bezel shows an even, light bulge all the way round.
Does a plain pushbutton need the anti-rotation key?
No — a pushbutton or toggle that nobody turns gets no key: the lock nut, the gasket's friction and a drop of removable threadlocker on metal threads hold the position, and the key slot sits unused on the bushing.
Switch makers often machine every bushing on one line, so the slot appears on plain buttons that will never use it. A rubber sealing washer under the nut supplies the friction in nearly all plain-button installs, which saves the second hole and the second drill operation per switch. Threadlocker belongs on metal threads; plastic nuts are usually self-locking, so skip it there. Where the side hole already exists in the panel, fit the washer anyway — it stops a working button ring from loosening over the years.
What keeps the holes sealed on a washdown panel?
The tongue hole is the leak: its Ø3 mm [0.12 in] mouth opens 7.1 mm² of panel while the tab blocks about 2.3 mm², so the bead of sealant under the washer must cover the near 5 mm² that stays open.
The arithmetic: π × 1.5² = 7.1 mm² of open mouth, a 1.5 mm wide tab covers roughly 1.5 × 1.5 = 2.3 mm², and 7.1 − 2.3 ≈ 4.8 mm² remains. A continuous bead under the washer, lapped over the tab and the web, closes it; a dry tab in a wet plant drips. The main hole seals on the switch's own gasket, so pick a switch whose front-of-panel rating matches the hose. The lowest-rated part in the wall sets the rating of the whole assembly. Our stainless boxes are rated NEMA 4X / IP66 by the manufacturer; not UL listed. Any piercing rated below the box drags the assembly down with it. The panel-mount switch sealing for washdown guide carries the full bezel detail, and the sealing a wrongly drilled hole guide rescues a hole that wandered.
What goes on the order?
Send one hole schedule per switch: a Ø16.2 mm [0.64 in] main hole and a Ø3.0 mm [0.12 in] tongue hole at 11.0 mm [0.43 in] center distance, both deburred on both faces — the finished box is delivered in 10 business days from your approval of the drawing.
- Holes: 1 × Ø16.2 mm [0.64 in] plus 1 × Ø3.0 mm [0.12 in] at 11.0 mm centers, edges deburred, no burr rolled into the gasket face.
- Material: 304 stainless for most washdown duty; 316L where salt, chlorides or sanitizers sit on the surface.
- Layout: draw the hole pair in the cutout designer and send it with the quote request.
- A door full of switches or a one-off body: start from the custom stainless page and its cutout drawing checklist.
- Fundamentals of holes, glands and display windows sit in the cutouts, glands and HMI windows guide.
Decision, in one line: buy the round punch and stop hunting for an inward-key die. Tongue washer for keyed bushings, double-D ring for flatted bosses, nut and gasket alone for a plain button — and no unsealed 3 mm hole in a panel that calls itself washdown.
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
What size hole do I drill for a 16 mm panel switch?
Drill 16.2 mm [0.64 in] for a slide fit, which is 0.2 mm of clearance over the 16 mm bushing. From a fractional set, 5/8 in (15.88 mm) is 0.12 mm tight on the bushing and needs a reamer; 21/32 in (16.67 mm) overshoots the 16.2 mm target by 0.47 mm. Pilot first and deburr both faces.
Will a tongue washer hold an emergency-stop's twist release?
Yes, when the tab sits in its 3 mm hole and the nut is snug. The steel tab carries the wrenching load that the 1.4 mm web between the holes was never meant to take, and a 40 mm [1.6 in] mushroom head puts an annoyed thumb 20 mm from the axis, so expect abuse.
Does the anti-rotation hole break a NEMA 4X rating?
Only if you leave the 3 mm mouth open. It exposes about 7.1 mm², the tab blocks roughly 2.3 mm², and the near 5 mm² remainder needs a sealant bead under the washer. The main hole seals on the switch's own gasket, so the switch must carry the front-side rating too.
Is there a punch for a double-D switch hole?
Yes — D and double-D punches are stock tools, unlike an inward-key punch, which would have to leave material standing in the hole. If the switch has flats and only round tooling is on the shelf, an anti-rotation ring with a double-D bore over a Ø16.2 mm round hole does the same job.
Can the side hole go at any clock position?
Yes — the tab rides anywhere on the washer's rim, so the slot's clock position follows the side hole you drill. Put the Ø3 mm hole where the panel legend needs the marked positions to read, often 12 o'clock, and orient the switch as you snug the nut.
