Surgical blade sizes, and what each one is for

Scalpel blades carry a numbering system that has nothing to do with size order and everything to do with shape. It came from surgery, where the number tells you what kind of cut a blade was ground to make, and it survives unchanged on blades sold for craft and model work because the shapes are just as useful there.

Learn the two families and the numbers stop looking arbitrary.

First, a warning about the numbers

Craft blade numbers and scalpel blade numbers are separate systems that happen to use the same digits. We sell a #10, #12, #15, #24 and #25 in both ranges, and in every case they are unrelated blades. An Excel #10 is a small curved craft blade for a K1 handle. A scalpel #10 is a broad bellied blade for a No.3 scalpel handle. They fit different handles and they are not alternatives to one another.

If you are following a tutorial, check which family it means before ordering.

The pointed blades

These cut at the tip. You pierce and draw, and the contact patch stays small, which is where the control comes from.

#11 is the one almost everyone means. A straight blade with a long fine point, for going in and cutting out along a line. It is the standard blade for masks and stencils, trimming prints, paper cutting, and any work where you are following a drawn line closely. If you buy one scalpel blade, buy this. It comes as ACM No.11 blades in fives, or on the Swann-Morton non-sterile range.

#12 is a small crescent, a hook with the cutting edge on the inside. It cuts on the pull, which suits anything you want to catch and sever rather than press through: threads, stitching, thin cord, and lifting an edge without cutting what is underneath. Find it on the surgical knife blades.

The bellied blades

These cut along a curve rather than at a point. The belly rolls through the material as you draw, so the cut stays continuous and the tip never digs in. They suit long cuts and sweeping shapes, and they are kinder to soft materials because nothing concentrates the pressure.

All of the numbers below are variants of the Swann-Morton non-sterile range.

• #10, the standard bellied blade: broad, curved, general-purpose. Good for leather, card, foam and anything cut to a shape rather than a line.
• #10A, a variation on the #10 with a straighter back and a less pronounced belly.
• #15, a #10 with a shorter, tighter curve. The smaller radius turns inside a smaller space, so it is the one for detailed curved work where a #10 is too long to follow the shape.
• #20, a larger #10 with a broad curve, for longer cuts with more force behind them.
• #23, a flatter curve, which holds a more consistent depth along a long cut.
• #24, close to a semicircle with a rounded tip, for long sweeping cuts with very little resistance.

The range also runs to #25 and #26 for larger work.

Handles

Scalpel blades are not interchangeable across handles. The blades above take a No.3 fitting, which is the one to buy first. We stock a graduated stainless No.3 handle on its own, or you can start with a set: a No.3 handle with #10A blades, or a stainless No.3 handle with a #11.

Larger blades in the twenties use a No.4 fitting on some ranges, so check the fitting rather than the number if you are mixing brands.

Changing blades safely

Scalpel blades are sharper than craft blades and thin enough to snap. Both matter when you are fitting one.

Lift the blade onto the handle from its blunt back edge, never by gripping the sides, and keep your fingers behind the cutting edge throughout. A blade remover is worth having if you get through blades in any quantity: it takes the used blade off and retains it, so you are neither prising at it with your fingers nor leaving a loose blade on the bench.

Used blades go into a sealed rigid container, never a bin bag.

Which to buy

For most people the answer is a No.3 handle, a packet of #11, and a few #10 for when the cut is a shape rather than a line.