In sheet metal, a hole is more than a feature. It is a cut through the material that leaves a thin "ligament" of metal around it, and that ligament has to carry the stresses of punching, forming, and later fastening. When the material left around a hole is too thin, it tears during punching, distorts during bending, or cracks under a loaded fastener. The minimum hole distance is the clearance that keeps the surrounding material strong enough to survive all of these stages.

The Quick Rules of Thumb

Manufacturers generally work from a small set of rules that scale with the material thickness, usually written as T. These are starting points, not fixed laws, but they cover the three distances that matter most.

Hole to Edge: Protecting the Weak Strip

When a hole sits too close to a free edge, the narrow strip of metal left between the two becomes the weak point of the part. During punching, that strip can tear or push burrs out onto the edge. During bending or under fastener load, the same strip can crack and slowly propagate over time. The practical rule is to keep the distance from the edge of the hole to the edge of the part at least 1.5 to 2 times the material thickness. On a 2.0 mm sheet, for example, that means roughly 3 to 4 mm of material should remain between the hole and the edge.

Hole to Bend: Where Holes Get Into Trouble

Bending is where holes most often fail. The material near the bend line stretches on the outside of the bend and compresses on the inside, so any hole that intrudes into that zone tends to distort as it is formed. Round holes become oval, and slot positions shift relative to their mating parts. To keep a hole round, place it at least 2 to 3 times the material thickness away from the bend line, measured from the bend line itself. If the bend radius is tight or the material is a hard, high-strength grade, adding extra clearance is the safer choice.

Hole to Hole: Keeping the Ligament Strong

When two holes are placed close together, the ligament of material between them weakens and can tear or crack, especially in thin or hard sheets. A minimum of about one material thickness between the edges of adjacent holes is a practical starting point. Note that the distance is measured from the edge of one hole to the edge of the next, not from center to center, because it is the ligament that carries the load.

Why the "Rules" Are Starting Points

These numbers are guidelines, not universal laws. The true minimum depends on the material grade and hardness, the sheet thickness, the forming process, and how the hole is made. Punching needs more edge support to prevent tearing, while laser cutting can hold tighter positions but may introduce heat effects in thin sections. Harder and thicker materials generally need more clearance. When a design is tight, the safest move is to review the geometry with the manufacturer during the DFM stage rather than assume a generic value will work.

This is exactly where a partner who builds the tooling as well as the parts earns its keep. A sheet metal part design that ignores hole clearance will look fine in CAD and fail on the press. DIAN STAMPING, a China-based manufacturer of automotive stamping dies, stamped sheet-metal parts, checking fixtures, and welding jigs, reviews these details before tooling is cut. With more than 20 years of experience serving OEMs such as KIA, BYD, Toyota, Honda, Suzuki, and Geely, the team helps customers catch placement problems early and turn drawings into parts that form correctly the first time.

Whether a project starts from a 2D drawing, 3D data, or a physical sample, the same attention applies. From custom sheet metal parts to fully developed stamping dies, keeping the minimum hole distance right from the start reduces rework, shortens lead times, and protects the long-term reliability of the assembly. When in doubt about a tight dimension, ask the manufacturer before the die is machined, because a few millimeters of clearance now is far cheaper than a failed run later.