ER25 Collet Set 1-16mm for CNC Router Tooling

An ER25 collet set is the clamping system used on ER25 spindles and tool holders to grip round-shank cutters securely during machining. Each collet has an outer diameter of 28mm and a length of 34mm, matching the ER25 nut and holder dimensions used on most CNC routers and milling spindles.

This range covers shank sizes from 1mm to 16mm, so it suits everything from small engraving bits to larger roughing end mills. It is aimed at CNC operators, cabinet makers and machine shops who need dependable, low-runout tool holding without investing in a different chuck for every cutter diameter.

Features

Every collet in this ER25 collet set closes uniformly around the cutter shank, spreading clamping force evenly across the full circumference. That even pressure keeps the cutter centred, improving surface finish and reducing the chance of a tool working loose mid-cut.

Because each collet only grips a narrow band of diameters, the set uses multiple sleeves rather than one adjustable part. Picking the wrong size, even by half a millimetre, means the collet won’t close on the shank or crushes it out of round, so matching collet to cutter matters.

• Outer diameter 28mm, length 34mm, standard ER25 dimensions
• Covers shank sizes from 1mm to 16mm across the set
• Even radial clamping force for low runout and reduced vibration
• Compatible with any spindle, chuck or tool holder using an ER25 nut
• Hardened steel construction for repeated clamping cycles

Where it’s used

ER25 collet sets are standard equipment on CNC router spindles, manual and CNC milling machines, and engraving heads that accept ER25 tool holders. They hold straight-shank end mills, drills, engraving bits and V-bits used to cut wood, MDF, acrylic, aluminium and composite panels.

Workshops that switch between fine detail work and larger cutting jobs benefit most, since one holder can accept collets across the full 1mm-16mm range instead of swapping the whole chuck. For the full range of compatible spindle accessories, browse the CNC tooling shop.

What to check before buying an ER25 collet set

Confirm the spindle or tool holder uses ER25 collets and not a different size such as ER11, ER16 or ER32 — the nut and collet pocket are not interchangeable between series. Measure the shank of the cutters you actually use, since buying sizes you’ll never need just wastes money.

Watch for cutter shanks that fall between standard sizes, such as 3.175mm (1/8 inch) tooling, which needs its own dedicated collet rather than the nearest metric size. Cheap collets that are out of round or poorly hardened cause runout, showing up as a rough edge finish or premature bit wear, so buy from a supplier that states these dimensions clearly.

Installation and maintenance

Fit the collet from your ER25 collet set into the ER25 nut before threading the nut onto the spindle nose, then insert the cutter and tighten with two wrenches, one holding the spindle shaft and one turning the nut. Avoid over-tightening once the collet has closed on the shank, as excess force can deform the collet’s slots and shorten its working life.

Keep the collet’s outer taper and the nut’s inner bore clean, since trapped dust or chips increase runout and can mark the cutter shank on removal. A light film of oil on the taper prevents corrosion between uses; for background on how this collet clamping principle works, see the general reference.

FAQ

Can one collet in an ER25 collet set clamp several cutter diameters? No, each collet only closes across a narrow range of about half a millimetre, so a full set is needed to cover 1mm to 16mm shanks.

Are ER25 and ER32 collets interchangeable? No, the two series have different outer dimensions and use different nuts, so a collet from one series will not fit a holder built for the other.

How do I know if a collet is worn out? Visible runout at the cutter tip, difficulty tightening the nut, or a collet that no longer grips evenly around the shank all indicate it should be replaced.

Which collet size should I choose? Every ER collet clamps securely over a 1mm range below its nominal diameter: the 4mm collet takes shanks from 3 to 4mm and the 6mm collet from 5 to 6mm. So for a 3.175mm (1/8″) cutter pick the 4mm collet, and for a 5mm shank the 6mm collet. Intermediate sizes not shown in the list are not kept in stock, but we bring them in on request — contact us.