Minimum Punched Hole Size by Sheet Thickness

A punch that is too small for the material can bend, wear quickly, or fail. The minimum also changes with the material and whether the punch is guided. This chart shows Mate Precision Technologies’ guidance for small round holes and its two tooling categories. Use the ratio for the row that matches the material and tooling, then confirm it with the actual punch supplier and press setup.

Minimum punch diameter by material and tooling

MECHANITEC / ENGINEERING REFERENCE

Minimum punch size by material and tooling

Mate Precision Technologies' guideline ratios for small round holes; use the actual press and tool maker's limits for a design release.

1–6 of 6 matching rows (6 total)

Minimum punch size by material and tooling — page 1 of 1
Material	Tooling category	Minimum punch / thickness ratio (d/t)	Example sheet thickness (mm)	Example minimum diameter (mm)	Same example (in)	Scope
Aluminum	Non-guided	0.75	2	1.5	0.059	Mate guideline; rounded example is about 1.50 mm (0.059 in).
Mild steel	Non-guided	1	2	2	0.079	Mate recommends a punch at least equal to material thickness for this tooling category.
Stainless steel	Non-guided	2	2	4	0.157	Mate recommends a punch about twice the material thickness for this tooling category.
Aluminum	Fully guided Mate tooling	0.5	2	1	0.039	Mate's fully guided tooling example; do not apply to non-guided tooling.
Mild steel	Fully guided Mate tooling	0.75	2	1.5	0.059	Mate's fully guided tooling example; consult Mate for the applicable product and station.
Stainless steel	Fully guided Mate tooling	1	2	2	0.079	Mate's fully guided tooling example; do not substitute the non-guided ratio.

Search and sort apply to all 6 rows. Print and CSV include only the 6 rows shown on this page.

How to calculate a starting diameter

For a round hole, multiply the sheet thickness by the ratio shown for the material and tooling category:

Minimum punch diameter = ratio × sheet thickness

For example, with 2 mm mild steel and non-guided tooling, the Mate guideline uses a ratio of 1. The starting minimum is therefore 1 × 2 mm = 2 mm. Its fully guided tooling guideline for mild steel is 0.75, which gives 1.5 mm for the same thickness. These are manufacturer-specific recommendations, not a universal approval to punch those features on any machine.

Why the ratio changes

The punch has to carry the force needed to shear the material. Material strength, thickness, tool geometry, punch support, die clearance, and the condition of the cutting edges all affect that force. A fully guided tool supports the punch differently from a non-guided setup, so Mate publishes separate ratios for the two categories. Do not apply the smaller fully guided values to a standard non-guided punch.

Material labels also matter. Mate’s stated non-guided ratios differ for aluminum, mild steel, and stainless steel. “Stainless” covers many grades and conditions, so the named row should be used only as an initial reference. A high-strength alloy, thick stock, unusual punch profile, or high-volume run may need a more conservative design or a different process.

Round holes and shaped openings

The formula in this article is for round-hole diameter. Mate also mentions narrow or wide-shaped tools, but a single diameter ratio does not fully describe a rectangle, slot, corner, or other profile. For a non-round opening, ask the tooling supplier which dimension controls the tool’s strength and what corner radii, clearance, and press capacity are required. Do not assume the round-hole ratio is a complete rule for every shape.

Before releasing a drawing

Use the sheet’s specified material grade and thickness, not just a generic label. Confirm the punch and die series, tool guidance, clearance, press tonnage, part support, hole-to-edge spacing, and the required hole tolerance. Mate separately recommends minimum spacing from nearby holes and edges; those layout checks are not included in the diameter formula above.

If a small opening is critical, send the drawing and material specification to the tooling supplier before production. Laser cutting, drilling, or a staged process may be a better option when the punch limit, hole quality, or required tolerance cannot be met reliably.

Source

The material-to-thickness ratios and example dimensions are from Mate Precision Technologies’ punching guidance. Mate describes the values as recommendations and asks users to consider their own application, machine, and tooling.