Router Collet Sizes Explained — 1/4", 1/2" & 8mm (2026 Guide)

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Router Collet Sizes Explained — 1/4″, 1/2″ & 8mm

The collet is the bit that grips your router bit’s shank and holds it in place while it spins at 20,000+ RPM. Get the wrong size and you’ve either got a bit that won’t fit, or worse — one that’s not gripped properly and could fly out mid-cut. This guide explains every collet size you’ll find on routers sold in the UK, which machines use which, and what to do if you’ve bought bits that don’t match your router.

The Three Main Collet Sizes

1/4″ (6.35mm) — The Compact Standard

The 1/4″ collet is the most common size on smaller routers. If you’ve got a palm router, trim router, or compact plunge router, there’s a very good chance it takes 1/4″ shank bits only. This includes popular models like the Makita RT0702C, DeWalt DWE6005, Bosch GKF 12V-8, and the Katsu range of trim routers.

Pros: Huge range of affordable bits available. Most decorative profiles, roundovers, chamfers, and straight cutters come in 1/4″ shank. Lighter weight means less stress on smaller motors.

Cons: The thinner shank flexes more under heavy loads. Not ideal for large-diameter cutters or deep cuts in hardwood. You’ll feel the vibration on bigger profiles.

Best for: Edge profiling, trimming, hinge recessing, small-to-medium joinery work, and general light-duty routing.

1/2″ (12.7mm) — The Professional Choice

The 1/2″ collet is what you’ll find on full-size plunge routers and any router designed for table mounting. This is the standard for professional and serious hobbyist woodworking. Models like the Makita RP2301FC, DeWalt DW625EK, Festool OF 2200, Bosch GOF 1600 CE, and Trend T12EK all come with 1/2″ collets (most also include a 1/4″ collet in the box).

Pros: Much stiffer shank means less vibration and cleaner cuts. Essential for large panel-raising bits, big roundovers, and heavy material removal. The extra mass absorbs vibration better.

Cons: Bigger bits are heavier and more expensive. You need a more powerful router to drive them — typically 1,400W minimum, ideally 2,000W+ for large profile bits.

Best for: Router table work, raised panels, large moulding profiles, template routing in hardwood, staircase work, and any job where cut quality and vibration matter.

8mm — The European Metric Standard

The 8mm collet is primarily associated with Festool routers (OF 1010, OF 1400, OF 2200) and some older Elu models. It’s a metric standard that never fully caught on outside continental Europe, which means fewer bit choices in the UK market.

Critical warning: 8mm is NOT the same as 1/4″. This trips people up constantly. The difference is 1.65mm — enough that a 1/4″ bit will sit loosely in an 8mm collet and won’t be gripped safely. Never try to force an 8mm bit into a 1/4″ collet either. The tolerances on router collets are measured in hundredths of a millimetre for good reason.

What to do if you have a Festool: Festool routers accept multiple collet sizes. The OF 1400, for example, can use 6mm, 8mm, 1/4″, and 1/2″ collets — you just need to buy the correct collet insert. This is one of the advantages of the Festool system.

Complete Collet Size Comparison

Collet Size	Diameter (mm)	Common Router Types	UK Bit Availability	Typical Power Range
1/4″	6.35mm	Palm routers, trim routers, compact plunge	Excellent	500W – 1,400W
8mm	8.00mm	Festool, Elu, some European brands	Limited	1,000W – 2,200W
3/8″	9.53mm	Rare US imports	Very limited	Varies
1/2″	12.7mm	Full-size plunge, router tables	Excellent	1,400W – 2,400W
6mm	6.00mm	Some Festool, Mafell, laminate trimmers	Limited	500W – 1,000W
12mm	12.00mm	Some European industrial routers	Very limited	1,800W+

Can You Convert Between Collet Sizes?

Yes — with limitations. The most common conversion is running 1/4″ shank bits in a 1/2″ collet router using a collet reducer (also called a reduction sleeve or collet adaptor). This is a small steel sleeve that fits inside your 1/2″ collet and reduces the bore to accept 1/4″ shanks.

What Works

Conversion	Method	Safety	Notes
1/4″ bit in 1/2″ collet	Collet reducer sleeve	Safe — widely used	Most common conversion. Trend, Axminster, and others sell these.
8mm bit in 1/2″ collet	8mm collet reducer	Safe — widely used	Lets you use European bits in imperial routers.
1/4″ bit in 8mm collet	Not recommended	Unsafe	The 1.65mm gap is too large for a reducer to work reliably.
1/2″ bit in 1/4″ collet	Impossible	N/A	The bit is physically too large. No adaptor exists.
6mm bit in 1/4″ collet	Not recommended	Risky	0.35mm difference — some try it, but concentricity is poor.

A good quality collet reducer from Trend or Axminster will set you back around £8-15 and will last years. The cheap ones off eBay and Amazon marketplace can have poor concentricity, which means the bit wobbles slightly and gives you a rougher cut. For occasional use they’re fine, but if you’re running 1/4″ bits in a router table all day, invest in a proper one.

See our full collet adaptor buyer’s guide for our recommended products.

Buy Trend 1/2″ to 1/4″ Collet Reducer on Amazon

How to Check Your Router’s Collet Size

If you’re not sure what collet size your router takes, there are a few ways to find out:

1. Check the manual or spec sheet. Every router lists the collet size in its specifications. If you’ve lost the paper manual, search for “[your model number] specifications” and you’ll find it on the manufacturer’s website or retailer product pages.

2. Measure the bore. Remove the collet from the router and measure the internal diameter with a ruler or callipers. 6.35mm = 1/4″, 12.7mm = 1/2″, 8mm = 8mm. If you don’t have callipers, try fitting a known bit — a 1/4″ bit from any standard set will tell you immediately if that’s the right size.

3. Use our brand tables. We’ve compiled collet sizes for every popular router sold in the UK. Find your router in our brand-by-model tables →

1/4″ vs 1/2″ — Which Should You Buy?

If you’re buying your first router and wondering which collet size to go for, here’s the honest answer: get a 1/2″ router that comes with both collets. Most mid-range and above plunge routers (£150+) include both a 1/2″ and 1/4″ collet in the box. This gives you full flexibility — you can run any bit on the market without needing adaptors.

If you’re only doing light trim work, edge profiling, or template routing on thin materials, a dedicated 1/4″ palm router makes sense as a second machine. They’re lighter, easier to control one-handed, and much less tiring for prolonged edge work. But as your only router? A 1/2″ machine with both collets is the way to go.