What Is a Collet?

A collet is a tapered metal sleeve that grips the shank of a rotating tool. As the handpiece nose cap is tightened, the collet compresses evenly around the shank, holding the bit centered and true. Each collet fits one shank size, so you swap collets when you change to a bit with a different shank.

Why a collet matters

A collet grips the entire circumference of the shank rather than at separate points. That even pressure does two things. It holds the bit centered, so the tool spins true, and it distributes the clamping force so the shank does not get marked.

Centering matters more than most people expect. A bit running off center vibrates, chatters against the work, wears unevenly, and puts strain on the handpiece bearings. At the speeds a rotary tool runs, small amounts of wobble show up in the finish and shorten the life of the bur.

Collet or chuck: which do you have?

Both hold a bit. They do it differently.

A collet is sized to one shank diameter and wraps around it completely, so the grip is even all the way around. You change collets when you change to a different shank size.

A three-jaw chuck closes three jaws onto the shank and handles any size within its range, so you can move between bits without swapping anything.

Neither is better. A collet gives you a dedicated fit for one size. A chuck gives you range. Both hold true, and which one suits you depends on whether you tend to work in one shank size or move between several.

For a fuller comparison, see What Is the Difference Between a Chuck and a Collet?

How Foredom handpieces hold bits

Foredom handpieces fall into a few groups, and which group yours belongs to determines everything about how you change bits.

Three-jaw chuck handpieces

The H.30 is the chuck-style handpiece. It accepts any shank from 1/16" up to 5/32" (4mm) with no collets and nothing to swap. You open the jaws with the chuck key, drop the bit in, tighten. That range covers the large majority of burs and accessories, which is why the H.30 is the usual recommendation for anyone working across many bit sizes.

It is also the handpiece that drives most Foredom accessories, including the drill press, angle grinder, belt sander and wax trimmers.

The H.30 variants work the same way on different shaft types: H.30H for square drive, H.30SJ for slip joint, and H.30-C2 as a keyless version.

Collet style handpieces

These use interchangeable collets, one per shank size. They give a dedicated fit for the size you are working in.

• H.44T and H.43T cover the widest range, 1/16" through 7/32" with the right collet. They include collets for 3/32" and 1/8", the two most common sizes, plus 1/4".
• H.28 and H.8 are the compact options, covering 1/16" through 1/8".
• H.25 is the heavy duty option, covering 1/16" through 1/4".

Collet sets are available so you do not have to buy sizes one at a time: HP440 for the H.44T and H.43T, HP600 for the H.28 and H.8, and HP103000 for the H.25.

Quick change handpieces

The H.10, H.18 and H.20 are built around 3/32" (2.35mm), the jewelry industry standard shank. They change bits faster than any other option, trading shank flexibility for that speed.

Collet adapters

An adapter is not a collet. It fits inside a collet you already have and lets you run a smaller shank without swapping collets. Foredom makes five:

• HPL4-3233 adapts 3/32" down to 1/16"
• HPL4-3234 adapts 1/8" down to 1/16"
• HPL4-3235 adapts 3.0mm down to 3/32"
• HPL4-3236 adapts 1/8" down to 3/32", the two most common shank sizes
• HPL4-3237 adapts 3.0mm down to 1.6mm

They also work with micromotor handpieces, and they are what let a quick change handpiece take a 1/16" shank. See all collet adapters

What size do I need?

Most bits and burs use one of two shank sizes:

• 3/32" (2.35mm) is the jewelry and dental standard. If you bought your burs from a jewelry supplier, this is almost certainly what you have.
• 1/8" (3.18mm) is common on wood carving burs and larger accessories.

If you are not sure, measure the shank with calipers before buying. Metric and imperial sizes sit close together, and 3mm is not the same as 3/32" even though the two are often used interchangeably.

Which collet fits my handpiece?

Every Foredom handpiece has its own set of compatible shank sizes, and which collets are included versus sold separately varies by model.

See the full shank size compatibility chart

The chart covers every handpiece, every shank size, and the collet part numbers.

Shop collets and handpieces

Collets

• HP440 set for the H.44T, H.43T and similar
• HP600 set for the H.8 and H.28
• HP103000 set for the H.25
• Collet adapters, all five sizes

Handpieces

• H.30 chuck style, the workhorse
• H.44T and H.43T collet style, widest range
• H.28 and H.8 collet style, compact
• H.25 collet style, heavy duty
• H.10, H.18 and H.20 quick change