Router shank sizes can be confusing because there are three common standards in use in the UK: 1/4 inch (6.35mm), 8mm, and 1/2 inch (12.7mm). Each has pros and cons, and each works with a specific set of routers. This guide explains the differences, when to choose each, and which brands favour each size.
Router Shank Sizes at a Glance
| Shank Size | Exact Diameter | Stiffness (relative) | Typical Routers | Typical Cutter Sizes |
|---|---|---|---|---|
| 1/4 inch | 6.35mm | 1.0× (baseline) | Palm routers, most mid-size plunge routers | Up to 35mm |
| 8mm | 8.00mm | 2.5× stiffer | Festool OF range, some Bosch Pro, Trend CraftPro | Up to 50mm |
| 1/2 inch | 12.70mm | 16× stiffer | Heavy plunge routers, router-table routers | Up to 120mm+ |
Note: stiffness scales with the fourth power of diameter, which is why 1/2 inch is so much stiffer than 1/4 inch, and why 8mm sits comfortably between them.
Buy Router Collet Sets on Amazon UK
1/4 Inch (6.35mm) Shank
The oldest and most common router shank size in the English-speaking world. Fits every palm router and all mid-size plunge routers either natively or with a reducer collet. Hundreds of profiles available, widely stocked by every UK retailer.
When to Use 1/4 Inch
Best for cutters up to around 35mm diameter — roundovers, chamfers, small rebates, edge-forming bits, V-groove bits, small straight cutters. Ideal for trim work, hinge mortises, sign-carving and light DIY use.
Limitations
Flexes under load on larger cutters. Not suitable for raised-panel work, heavy rebates, or production cutting. Skip 1/4 inch for any cutter over 35mm diameter.
8mm Shank
The European compromise. Introduced and pushed by Festool as a standard, also offered by Trend (CraftPro range), some Bosch Professional bits, and specialist brands like CMT and Whiteside. 2.5× stiffer than 1/4 inch but only marginally larger in diameter.
When to Use 8mm
If you own a Festool router (OF 1010, OF 1400, OF 2200), the default collet is 8mm and you’ll find a large 8mm bit range. Offers better stiffness for cutters up to around 50mm, a sweet spot for hardwood and laminate work.
Limitations
Smaller selection than 1/4 inch or 1/2 inch in the UK. More expensive in general. Not compatible with routers that only offer 1/4 and 1/2 inch collets unless you buy an 8mm collet separately (available for most DeWalt, Makita, Bosch, Triton routers).
1/2 Inch (12.7mm) Shank
The professional standard. Essential for heavy cutters, raised-panel work, and router-table use. Roughly 16× stiffer than 1/4 inch, meaning virtually no measurable deflection under normal loads. Every heavy plunge router (2000W+) accepts 1/2 inch.
When to Use 1/2 Inch
Anything above 35mm cutter diameter, plus production work, hardwoods, MDF, and anything that needs to run on a router table. All large profile cutters — raised panels, lock-mitre, stile-and-rail — are only safely made on 1/2 inch.
Buy 1/2 inch Router Bit Set on Amazon UK
Limitations
Won’t fit palm routers (1/4 inch only) or routers that don’t offer a 1/2 inch collet. Bits are slightly more expensive per profile.
Which Brands Use Which Shank?
| Brand | 1/4 inch | 8mm | 1/2 inch |
|---|---|---|---|
| Makita | Yes (trim + all plunge) | Optional collet | Yes (3612C, RP2301FCX) |
| DeWalt | Yes (all routers) | Optional collet | Yes (DW625EK, D26204K) |
| Bosch | Yes | Yes (some bits + GOF 1600) | Yes (GOF 1600 CE) |
| Festool | Optional collet | Default | Optional collet (OF 2200) |
| Trend | Yes (T4, T5) | Yes (CraftPro) | Yes (T7, T11, T14) |
| Triton | Yes | Optional | Yes (TRA001, MOF001) |
| Freud | Yes | Limited | Yes |
Can I Use Reducer Collets?
Yes, but with caveats. Reducer sleeves drop into a larger collet to let you use smaller shanks. The most common setup is a 1/4 inch reducer in a 1/2 inch collet — this is standard kit with virtually every 1/2 inch router sold in the UK.
Reducer sleeves work fine for light to medium work but introduce a small amount of runout compared to a proper same-size collet. For heavy production work, use a purpose-made 1/4 inch or 8mm collet instead.
Where to Buy
Buy Mixed Shank Router Bit Set on Amazon UK
For detailed brand compatibility, see our router bit compatibility hub. For collet selection, read our router collet compatibility guide, or compare sizes directly in 1/4 vs 1/2 inch router bits.
Frequently Asked Questions
What is the difference between 6mm and 1/4 inch router bits?
1/4 inch is 6.35mm — 0.35mm larger than 6mm. Though close, they are not interchangeable. A 6mm bit will be loose in a 1/4 inch collet and may slip; a 1/4 inch bit will not fit a 6mm collet at all.
Why do Festool routers use 8mm?
Festool standardised on 8mm across European markets as a compromise between 1/4 inch flexibility and 1/2 inch stiffness. Their OF 1010, OF 1400 and OF 2200 routers ship with 8mm collets as default; 1/4 inch and 1/2 inch collets are sold separately.
Can I use an 8mm bit in a 1/4 inch collet?
No. 8mm is larger than 6.35mm (1/4 inch), so the bit physically will not fit. You need an 8mm collet, which is available for most major router brands as an optional accessory.
Which shank size is best for router table use?
1/2 inch is the professional standard for router tables because larger cutters are needed for raised panels, stile-and-rail joinery and cope cuts. The extra stiffness also reduces chatter on the heavier cuts typical of table routing.
Are 8mm router bits easy to find in the UK?
Yes, particularly from Trend (CraftPro range), Festool, some Bosch Professional bits, and specialist tool merchants. Amazon UK and Axminster stock a wide range. Less common than 1/4 inch or 1/2 inch but perfectly available.
Do I need all three shank sizes?
Probably not. Most UK users get by with 1/4 inch and 1/2 inch. 8mm is mainly relevant if you own a Festool router or want to standardise with European tooling.