What Size Shank Does a Die Grinder Use?

Most die grinders use a 1/4 inch (6.35 mm) shank, and that is the size nearly every standard burr and abrasive point is made for. Smaller mini grinders use a 1/8 inch (3.175 mm) shank, and some tools sold in metric markets use 6 mm, which is close enough to 1/4 inch that the two are often treated as the same. The collet in your grinder sets the size, so check it before you buy bits.

The short version: 1/4 inch is the standard

The shank is the smooth round shaft on the back of a burr, stone or mounted point. It slides into the grinder's collet, and the collet squeezes it tight when you tighten the nut. For a standard die grinder, that shaft is 1/4 inch across, or about 6.35 mm.

That is why bit packs say things like "1/4 in shank fits most die grinders." If you are starting out and buying one set of burrs, 1/4 inch gives you the widest choice of shapes, sizes and materials.

Mini die grinders and some detail tools use a 1/8 inch shank instead. These bits are thinner and made for fine work, such as small ports, engraving and delicate deburring.

Shank sizes at a glance

Here is how the common sizes compare. The collet is the part you need to match, not the cutting head of the bit.

Shank size	Metric	Typical grinder	Best for
1/4 in	6.35 mm (often listed as 6 mm)	Standard die grinders, straight and right-angle	General grinding, deburring, shaping, porting
6 mm	6 mm	Metric-market grinders, some with dual collets	Same jobs as 1/4 in, with a tiny size difference
1/8 in	3.175 mm	Mini die grinders and tools with a second collet	Fine detail, small holes, light polishing
3 mm	3 mm	Some mini and rotary tools	Very small bits, often close to 1/8 in

What the grinders in our comparison use

The published specs on our best die grinder page show how common these sizes are. The Ingersoll Rand 3107G and 307B list a 1/4 in collet. The Chicago Pneumatic CP872 lists 1/4 in (6.4 mm) and 6 mm collets.

The WORKPRO W182004A and the KJE right-angle kit each list both 1/4 inch and 1/8 inch collets. That means one tool can hold standard burrs and also finer detail bits once you swap the collet.

If you run compressed-air tools, our best air die grinder page lists collet sizes next to speed and weight, so you can filter by the shank you already own.

What shank does a Milwaukee die grinder use?

We do not have published specs for a Milwaukee die grinder in our product data, so we cannot quote an exact figure for a particular model. In general, full-size die grinders from major brands, Milwaukee included, are built around a 1/4 inch collet, since that is the industry standard.

Some compact or specialty models may come with other collet sizes, or with extra collets in the box. The reliable way to know is to read the collet size on the tool's spec sheet or manual, or look at the collet itself.

If the manual lists a 1/4 inch collet, any 1/4 inch shank bit will fit. If it lists a 6 mm collet, 1/4 inch bits usually still seat, but a collet and shank that match exactly always grip best.

How to confirm the shank size on your tool

You do not have to guess. A few quick checks will tell you what size you have.

Always disconnect the air hose or remove the battery before you reach for the collet nut.

Read the spec sheet or manual. Look for "collet size" or "collet capacity."
Look at the collet nut or collet body. Many are stamped with 1/4, 6 mm or 1/8.
Measure a bit shank with calipers. A reading near 6.35 mm is 1/4 inch, and near 3.2 mm is 1/8 inch.
Check the bit packaging. The shank size is usually printed next to the head size.
Test with a spare bit while the tool is off and disconnected. It should slide in smoothly, with no wobble and no forcing.

Matching bits to your grinder

Once you know the shank, the next question is the bit itself. Carbide burrs cut metal fast and clean, while stones and abrasive points finish and polish. Our best die grinder bits for metal page compares options by shape and cut so you can choose for the job.

Use the shank that matches your collet. Do not wrap tape or shim a smaller shank into a larger collet. A bit that is not held properly can slip, wobble or fly out at high speed.

Insert the shank deep enough that most of it sits inside the collet, but do not bottom it out against the back. Leave a small gap, and keep the exposed neck short for less vibration.

Safety notes before you change bits

Die grinders spin fast. The grinders in our comparison run from 25000 to 28000 RPM, so a poorly seated bit becomes dangerous quickly.

Wear safety glasses or a face shield every time. Metal chips, sparks and broken bits can cause serious eye injuries. Hearing protection is also sensible, because pneumatic tools can be loud for long sessions.

Disconnect air or power before changing a bit or collet, and tighten the collet nut with the correct wrench. Check that the bit is rated for the tool's free speed, and never run a damaged or bent bit. Keep loose sleeves and hair away from the spinning head, and hold the work firmly.

Frequently asked questions

Can I use a 1/4 inch bit in a 6 mm collet?

They are very close in size, and many tools sell both as compatible. Still, a collet grips best when it matches the shank exactly, so use the size printed on the collet whenever you can.

Can I use a 1/8 inch bit in a 1/4 inch collet?

Not directly. The collet will not clamp a thinner shank safely. Use a grinder that includes a 1/8 inch collet, or buy the matching collet for your model.

Is the shank size the same as the bit head size?

No. The shank is the shaft that goes into the collet. The head is the cutting part, and it can be much larger or smaller than the shank.

Do air and electric die grinders use the same shank size?

Mostly yes. Both commonly use 1/4 inch collets, with 1/8 inch common on mini tools. Always confirm against your tool's own specs.