ER20 Collets – Precision Clamping 1mm to 13mm

ER20 collets are the clamping sleeves that hold cutting tools inside ER20 spindles, chucks, and tool holders. They cover a shank range from 1mm to 13mm, so a single collet set lets a workshop switch between drill bits, end mills, and engraving tools without changing the spindle nut or holder.

This collet standard is common on CNC routers, milling machines, and manual milling heads used by cabinet makers, sign shops, and metalworking shops. Anyone running an ER20 spindle needs a matching set of ER20 collets sized to the shanks they actually cut with, since each collet grips only one diameter reliably.

Features of ER20 Collets

Each collet in the ER20 range has a fixed internal bore that matches one shank diameter, with sizes spanning 1mm to 13mm in small increments. The collet body is a hardened steel sleeve with longitudinal slots that let it close evenly around the tool shank as the collet nut is tightened, so the tool sits on centre rather than off to one side.

The outer taper of the collet seats inside the ER20 nut and spindle nose, and this taper converts the axial force of tightening into uniform radial clamping pressure. Because the taper geometry is standardised, collets from different batches or brands generally interchange within the same ER20 nut, provided the nut and collet come from the same size family.

• Bore sizes from 1mm to 13mm, sold individually per size
• ER20 taper and outer diameter for standard ER20 nuts and spindles
• Hardened steel construction for repeated clamping cycles
• Slotted collet body for even radial closure around the shank
• Interchangeable within the ER20 size standard

Where ER20 collets are used

ER20 collets are fitted on CNC router spindles, ER20 milling chucks, and some manual milling machine heads. Workshops cutting wood, plastic, aluminium, and composite panels use them to hold router bits and end mills, while smaller sizes near the 1mm end suit engraving cutters and small drills used on signage and PCB work.

Because the range covers such a wide span of shank diameters, a shop can stock a handful of ER20 collets and cover most of its tooling without buying a second chuck. For a broader selection of spindle accessories and cutting tools alongside these collets, see the CNC tooling shop.

What to check before buying

Confirm the shank diameter of the tool first, then order the matching collet size. ER20 collets clamp reliably only at their stated size, not a range around it, so a shank that is even slightly undersized leaves the collet loose and off-centre. That shows up as chatter, poor surface finish, or a tool slipping under load.

Also check that the collet nut and spindle are genuinely ER20, since ER11, ER16, and ER25 collets look similar but are not interchangeable with an ER20 nut. Buyers replacing a worn collet should also check the collet seat and nut threads for wear, since a damaged nut can prevent even a new collet from clamping correctly.

Installation and maintenance

Fitting a collet is straightforward: insert it into the collet nut until it clicks into the retaining groove, slide the tool shank in to the recommended depth, then tighten the nut onto the spindle thread. Overtightening beyond the torque the collet needs can distort the bore over time, so it is worth checking general collet tightening guidance where the tool or spindle manufacturer does not specify a figure.

Keep collets clean and lightly oiled, and wipe down the taper and bore after use to remove dust and chips that can throw off concentricity. Worn or dropped collets should be replaced rather than reused, since a bent or damaged slot no longer closes evenly and will run the tool off centre even when tightened correctly.

FAQ

What size range do ER20 collets cover? The ER20 standard covers shank diameters from 1mm to 13mm, with each collet sized for one specific diameter.

Can I use an ER20 collet with an ER16 nut? No. ER20, ER16, and ER25 collets have different outer tapers and are not interchangeable between nut sizes.

How do I know when to replace a collet? Replace a collet if it looks worn, bent, or no longer grips a correctly sized shank tightly and concentrically.