Choosing a Screw-Punch Blade Size

Eight Needles Journal · Punching & finishing

A screw-punch blade determines the nominal hole size. The right choice comes from the project requirement, not from selecting the largest range of blades. Begin with the fitting, thread or construction instruction that the hole must serve.

Nonaka screw punch making. Photo from the Eight Needles collection.

Identify the requirement

Check any hardware manufacturer's hole specification and test the actual combination. Do not assume the outside diameter of a fitting is the correct hole measurement. Paper, leather and fabric can respond differently around an opening.

Make a labelled sample

Punch representative scrap with the selected blade using the tool's recommended method. Label the blade size and inspect the result. Try the intended fitting only as its instructions permit, without forcing it through an unsuitable hole.

Keep blades identifiable

Store each blade with its size and compatibility information. Similar-looking small parts are easy to mix once packaging is discarded. Add another size when a real project requires it rather than treating the full range as a necessary first purchase.

A practical example

A fitting's instructions specify a hole size. Start with that requirement and test the intended material and fitting together. Do not select the blade simply by measuring the fitting's widest outside edge; the required opening may be different.