A Midwest automation integrator sent us a control-panel drawing last quarter that looked fine in CAD. Three DIN rails, ten 22 mm push-button cutouts, a 12-position D-sub cutout on the lid, and four M20 knockouts on the bottom. The drawing was released. The prototype was built. Then the first article failed the in-house inspection for three reasons: the 22 mm cutouts were 22.8 mm (so the buttons seated crooked), the D-sub cutout was 16.4 mm wide (so the connector shell did not seat), and the M20 knockouts were too close to the bend line (so the laser edge cracked when the panel was brake-formed). The fix was tolerance tightening, cutout-to-edge spacing, and a different hole-to-bend clearance rule. The redesign took 5 days. The customer's delivery slipped two weeks. Below is the DFM playbook that would have prevented all three.
This guide covers DIN rail & panel cutout design for sheet metal enclosures: TS35 rail sizing (EN 60715), 22 mm push-button cutout (IEC 61554 / DIN 43700), D-sub / RJ45 / USB / HDMI patterns, M / PG / NPT knockout geometry, 19" rack cutouts (IEC 60297-1 / EIA-310-D), and IP seal design at cutout boundaries. Nine DFM rules at the end close the article.
Why DIN Rail & Cutout Standards Exist
An enclosure for industrial control, data acquisition, telecom, or building automation has to accept a standardized set of mounting rails and panel cutouts. Without standards, every enclosure would be a one-off and every component supplier would have to inventory custom brackets. The standards ecosystem in this space is older than the sheet metal industry itself — the 35 mm DIN rail dates to the 1920s in German electrical cabinets, and the 22 mm push-button cutout dates to the 1960s. Today they are codified as EN 60715 (TS35), IEC 61554 / DIN 43700 (22 mm), IEC 60297-1 / EIA-310-D (19" rack), and IEC 62080 / NEMA 5-15 (standard power outlet cutouts).
Two takeaways from the standard bodies for the sheet metal designer: (1) the cutout dimensions are nominal, but the tolerance band is wide enough that a sloppy fabrication will produce a connector that does not seat. Standardize on a tighter band (typically ± 0.1 mm) and document it on the drawing. (2) cutouts at the wrong location — too close to a bend line, too close to a weld, off-center on a face — are the single biggest source of rework on a control enclosure. For the broader control-panel context, see our control-panel enclosure guide, and for HMI displays, see our HMI enclosure design guide.
TS35 DIN Rail Sizing & Layout (EN 60715)
The 35 mm DIN rail (TS35, EN 60715, also referenced as DIN rail or top-hat rail) is the most common mounting rail inside a sheet metal control enclosure. There are three common profile depths — 7.5 mm (TS35/7.5), 15 mm (TS35/15), and the asymmetric 35 × 7.5 asymmetric profile (TS35/AS) for terminal blocks — and all share the same 35 mm outer width. The depth choice is mostly a function of how much weight the rail has to carry and how stiff you need it to be.
Sizing the rail length follows a five-step procedure:
- List every device. Terminal blocks (typically 5–10 mm wide), circuit breakers (17.5–36 mm wide), power supplies (typically 72–157 mm wide), PLCs, relays, signal conditioners, I/O blocks. Each has a published width.
- Sum the widths. Add up the widths of every device, plus 5–10 mm of clearance between devices for wiring.
- Round up to the next standard length. EN 60715 rails are stocked in 1 m, 0.5 m, and 0.25 m lengths; cut-to-length rails are common in OEM enclosures. Pick the next standard length up, not down.
- Add end stops. Each rail needs an end stop on each side to prevent sideways movement under wiring push or vibration; end stops add 8–10 mm each. For the vibration-resistant end stop on populated panels, see our fastener selection guide.
- Add a service loop. Reserve 50–80 mm of empty rail at one end for future expansion. Most customers add at least one device in the first year of service.
| Profile | Depth | Typical load (kg/m) | Best fit |
|---|---|---|---|
| TS35/7.5 | 7.5 mm | ≤ 5 kg/m | Light: small terminal blocks, signal relays |
| TS35/15 | 15 mm | ≤ 15 kg/m | Medium: power supplies, breakers, larger terminals |
| TS35/AS (asymmetric) | 7.5 mm | ≤ 5 kg/m | Terminal block alignment: prevents terminal blocks from tilting under wiring torque |
Mounting the rail to the back panel is typically by two M5 or M4 self-tapping screws into a captive nut (weld nut, clinch nut, or rivet nut) — never by self-tappers directly into thin sheet. For the related cable-gland-to-enclosure pattern, see our cable gland selection guide.
22 mm Push-Button Cutout (IEC 61554 / DIN 43700)
The 22 mm push-button cutout is the round hole that accepts an industrial push button, selector switch, indicator light, or emergency stop. The nominal diameter is 22.5 mm (IEC 61554 / DIN 43700), with a tolerance band that the standard sets at +0.4 / -0.0 mm. Practical fabrication tolerance is ± 0.1 mm; looser than that and the button seats crooked or falls through. The standard pattern for a single round cutout is the only relevant detail — multiple 22 mm cutouts are just that pattern repeated at the spacing required by the human-machine interface.
Three engineering rules cover 22 mm cutouts:
- Center-to-center spacing ≥ 30 mm. Buttons placed closer than 30 mm center-to-center interfere with each other at the bezel ring.
- Edge-to-edge spacing ≥ 11 mm. The cutout edge should be at least 11 mm from any bend line, panel edge, or weld seam. Closer than that, and the panel cracks at the bend.
- Tolerance ± 0.1 mm or tighter. Standard ± 0.2 mm fabrication tolerance will produce buttons that look crooked in a bezel-tight build. Specify ± 0.1 mm or use a fixture during punching.
D-Sub, RJ45, USB, HDMI Cutout Patterns
Data and signal connectors have standardized cutout patterns that the connector manufacturer publishes in the datasheet. The patterns vary widely; the design rule is to match the cutout to the exact datasheet pattern for the connector family, not to a generic round or rectangular hole.
| Connector family | Cutout pattern | Typical size | Tolerance | Notes |
|---|---|---|---|---|
| D-sub 9-pin (DE-9) | Trapezoid with two 3 mm screw holes at 16.33 mm centers | 16.6 × 30.8 mm body cutout + 2 × Ø 3.05 | ± 0.1 mm on body, ± 0.05 mm on screw holes | Standard for serial RS-232 / RS-485 |
| D-sub 25-pin (DB-25) | Trapezoid with two 3 mm screw holes at 47.04 mm centers | 16.6 × 53.0 mm body + 2 × Ø 3.05 | ± 0.1 / ± 0.05 mm | Standard for parallel / legacy serial |
| D-sub 15-pin HD (VGA) | Trapezoid with two 4-40 UNC jackscrew holes | 15.9 × 31.3 mm body + 2 × Ø 2.95 | ± 0.1 / ± 0.05 mm | Standard for VGA / analog RGB |
| RJ45 (Cat 5/6/7 keystone) | Rectangular with two side retention tabs | 14.6 × 19.3 mm body | ± 0.1 mm | Keystone jack snaps in; cutout varies by jack family |
| USB Type-A / Type-B | Rectangular with two side retention tabs | 14.0 × 6.5 mm body | ± 0.1 mm | Standard for USB 2.0 / 3.0 panel mount |
| USB Type-C | Oval with two side retention tabs | 9.0 × 7.4 mm body | ± 0.1 mm | Newer; symmetrical orientation |
| HDMI Type-A | Trapezoid with two side retention tabs | 15.0 × 6.0 mm body | ± 0.1 mm | Standard for HDMI panel mount |
| DisplayPort | Irregular trapezoid | 15.0 × 6.0 mm body (similar to HDMI) | ± 0.1 mm | Some overlap with HDMI mechanically |
| LC / SC fiber | Rectangular / square | 13.5 × 9.5 mm (LC duplex), 14.6 × 14.6 mm (SC simplex) | ± 0.1 mm | For telecom enclosures; see our telecom enclosure guide |
The rule for connector cutouts is: do not draw the cutout from memory. Pull the cutout pattern from the connector manufacturer's datasheet, and put the cutout into a separate DXF file that the fabricator uses for laser or punch programming. A 0.5 mm error on a D-sub trapezoid will not seat the connector.
Knockout / Conduit Holes (M / PG / NPT)
Conduit entries on the bottom or side of an industrial enclosure follow three thread families: metric (EN 50262 / IEC 62444), PG (Panzergewinde, the older European standard), and NPT (the US tapered pipe thread). Each has a standard hole size for the panel cut.
| Thread | Hole diameter for clearance fit | Hole diameter for tapped thread in sheet | Typical cable range |
|---|---|---|---|
| M12 × 1.5 | Ø 12.5 mm | Ø 10.6 mm (coarse sheet metal tap) | 3–7 mm |
| M16 × 1.5 | Ø 16.5 mm | Ø 14.5 mm | 5–10 mm |
| M20 × 1.5 | Ø 20.5 mm | Ø 18.5 mm | 7–13 mm |
| M25 × 1.5 | Ø 25.5 mm | Ø 23.5 mm | 10–17 mm |
| M32 × 1.5 | Ø 32.5 mm | Ø 30.5 mm | 13–21 mm |
| M40 × 1.5 | Ø 40.5 mm | — (use locknut) | 18–28 mm |
| M50 × 1.5 | Ø 50.5 mm | — | 27–35 mm |
| PG7 | Ø 13.0 mm | Ø 11.0 mm | 3–6.5 mm |
| PG9 | Ø 15.5 mm | Ø 13.5 mm | 4–8 mm |
| PG11 | Ø 19.0 mm | Ø 17.0 mm | 5–10 mm |
| PG13.5 | Ø 21.0 mm | Ø 19.0 mm | 6–12 mm |
| PG16 | Ø 23.0 mm | Ø 21.0 mm | 10–14 mm |
| PG21 | Ø 29.0 mm | Ø 27.0 mm | 13–18 mm |
| PG29 | Ø 37.5 mm | Ø 35.5 mm | 18–25 mm |
| PG36 | Ø 47.5 mm | — | 22–32 mm |
| NPT 1/2" | Ø 22.0 mm (clearance for tapered thread) | Ø 21.0 mm (taper tap) | 9–14 mm (with NPT gland) |
| NPT 3/4" | Ø 27.5 mm | Ø 26.5 mm | 13–18 mm |
| NPT 1" | Ø 34.5 mm | Ø 33.5 mm | 18–25 mm |
Three engineering rules for conduit knockouts:
- Center-to-center spacing ≥ 1.5 × hole diameter. Closer than that, the bridge between the two holes is too narrow to support a gland and the panel cracks at the bend.
- Edge-to-edge ≥ 1 × hole diameter. A hole drilled too close to a bend line or a panel edge cracks during forming. The rule of thumb is at least one hole-diameter of material between the hole and the nearest bend.
- Round the rectangular knockout with a corner radius ≥ 1 × thickness. A sharp internal corner is a stress concentration that cracks under vibration or impact. For the vibration side, see our vibration testing guide.
19" Rack Panel Cutout (IEC 60297-1 / EIA-310-D)
The 19" equipment rack (IEC 60297-1 / EIA-310-D) defines a panel face that is 482.6 mm wide (the "19 inches" refers to the inner rail spacing of 465.1 mm plus the ear flange on each side) and a 1U vertical pitch of 44.45 mm. The cutout pattern depends on the equipment family: a 1U blank panel is a flat rectangle; a 1U vented panel is the same rectangle with a perforation pattern; a 1U panel-mount equipment face is the rectangle with the equipment-specific cutouts (display, button, connector) inside it.
Three engineering rules for 19" panels:
- Use EIA-310-D hole pattern for cage nut retention. The full dimensional breakdown, including the U boundary and the thread options, is in our 19 inch rack dimensions guide. The standard 9.5 × 9.5 mm square hole (or M6 round hole) on the front flange, with vertical spacing 44.45 mm and horizontal spacing 465.1 mm inner / 482.6 mm outer.
- Specify 1U, 2U, 3U as vertical multiples of 44.45 mm. Half-U is 22.225 mm; quarter-U is 11.1125 mm. Custom heights between the standard increments will not fit standard rack-mount hardware.
- For thermal venting, use the EIA-310 vent pattern. A 1U vented panel typically has 60–70% open area. The pattern is 3 mm round holes on a 5 mm staggered grid, or stamped hexagonal holes. For the thermal side of vented panels, see our thermal management guide.
Maintaining IP Rating at Cutouts
A cutout is a hole. A hole is the failure point for ingress protection. The IP rating (IP54, IP65, IP66, IP67, IP68) of an enclosure is only as good as the weakest cutout. Three engineering rules carry most of the IP design:
- Use a gasket between the connector shell and the panel. Most panel-mount connectors (D-sub, RJ45, USB, HDMI) come with an integrated gasket. Verify that the connector datasheet specifies an IP rating with the gasket installed.
- Use a sealed cable gland on every conduit entry. A bare knockout hole is IP00. A standard cable gland with an O-ring at the panel interface is IP65 / IP68 depending on the gland rating. For the cable gland selection process, see our cable gland selection guide.
- Apply a bead of silicone sealant around the cutout edge for outdoor enclosures. For IP66 / IP67 outdoor enclosures, a 2 mm bead of RTV silicone around the cutout edge, under the gasket, adds a second line of defense against moisture wicking along the connector-panel interface. See our outdoor IP enclosure guide for the outdoor stack-up.
DFM — Common Cutout Mistakes
These nine DFM rules cover the rework we have seen on real programs. They are listed in priority order — the first three account for most of the cutout-related rejections we have seen.
- Cutout too close to a bend line. A cutout closer than 1 × its diameter to a bend line cracks when the panel is brake-formed. Specify the bend line first, then place cutouts ≥ 1 diameter away.
- Cutout too close to a panel edge. A cutout closer than 1 × its diameter to the panel edge is on the "tear-out" zone. The panel cracks at the edge during punching or in service under vibration. Specify the panel size first, then place cutouts.
- Tolerance too loose for the connector family. ± 0.2 mm tolerance is standard laser-cutting tolerance. For 22 mm push-buttons, D-sub shells, RJ45 keystones, and HDMI / USB cutouts, this is too loose. Specify ± 0.1 mm (or tighter) on cutouts that interact with a mating connector.
- Cutout at a weld seam. A cutout that crosses a weld seam leaves the seam partially exposed and breaks any gasket seal. Move the cutout away from the seam by ≥ 5 mm, or specify the cutout to be placed before the welding step.
- No corner radius on rectangular cutouts. A rectangular cutout without a corner radius is a stress concentration. Specify a corner radius ≥ 1 × material thickness for all rectangular cutouts.
- Cutout size for the cable, not for the gland. A common mistake is to drill the hole for the cable diameter, then try to fit a cable gland into the same hole. The gland body is larger than the cable. Drill for the gland body diameter, not the cable diameter. See the knockout table in Section 5.
- Adjacent cutouts too close together. Two cutouts closer than 1.5 × the larger hole diameter leave a bridge between them that is too thin to support a gland or a connector. Increase the spacing.
- Forgetting the gasket groove. A gasket requires a groove or a flat surface to seat in. A cutout on a curved surface (e.g. the side of a bent panel) does not give the gasket a flat sealing surface. Specify the cutout on a flat zone of the panel.
- Not specifying the cutout direction. Some cutouts (D-sub trapezoid, HDMI, USB Type-C) are directional. Drawing the cutout as a "rectangle" loses the direction. Specify the orientation with a witness mark or an arrow on the drawing.
For the broader DFM framework that these cutout rules sit inside — bend allowances, tolerance stacks, tool access — see our DFM design guide, and for the prototype-to-volume handoff on cutout-critical programs, see our prototype-to-production guide.
The SanJun Cutout Workflow
For OEM customers with cutout-critical enclosures, we run a four-step workflow:
- Cutout datasheet collection. For every connector, gland, display, or control device on the panel, we pull the cutout pattern from the manufacturer's published datasheet. The patterns are stored in a single DXF reference file that the laser programmer uses.
- DFM review. We run the 9 DFM checks above and flag any item that will cause rework. Most programs need 1–2 iterations before the drawing is releasable.
- First-article cutout inspection. We measure every cutout on the first article with a pin gauge or a calibrated optical comparator. The cutout log goes to the customer before production starts.
- Lot cutout inspection. We sample-cutout-inspect every production lot at AQL 1.5–2.5 (depending on the connector criticality). Cutout measurements are recorded in the lot FAI.
The output of the workflow is a documented cutout specification pack — cutout patterns, tolerances, edge spacing, gasket stack-up — that goes with every shipment and lets the customer's receiving inspector verify the lot without redrawing the geometry.
Conclusion
A sheet metal enclosure is defined by its cutouts. Get the cutouts wrong and the connectors do not seat, the glands do not seal, the buttons sit crooked, and the panel cracks at the bend. Get them right and the enclosure disappears into the system. The 9 DFM rules above cover the rework we have seen; the standards tables above cover the geometry. If you are at the RFQ stage, send us your device list and your preferred connector family. We will return a one-page cutout spec pack — TS35 rail length, cutout patterns, tolerances, gasket stack-up, FAI checklist — within 24 hours.