I need to fit some edge trim to various bits of furniture board in my camper van.

This is the correct router piece:


Bought, ordered, on its way.

Now I need a router. But almost all I look at are either 1/4" or 1/2". I can find ONE by Makita that says 8mm on it:


I've never used a router before, I've no idea if it's like a drill, and the chuck is infinitely adjustable up to its maximum size.... or if I NEED an 8mm router to go with an 8mm bit. If so, how come loads of people seem to make 8mm bits, but I can only find one make/model of 8mm router?

Thank you!

  • 4
    Here's an Amazon search that will get you the 3mm slot cutter you desire. It has bits with 6mm, 1/4", 8mm and 1/2" shanks. Get the bit that fits the router of your choice. Buy one quality router, then buy bits to match it, not the other way around.
    – FreeMan
    Jun 21, 2022 at 17:25
  • 1
    Also, you may want to check out Woodworking for wood working related questions.
    – FreeMan
    Jun 21, 2022 at 17:40
  • 4
    "I've never used a router before" Please be very careful. Routers don't behave like drills or saws. The cutting force is sideways along the face of the stock that the plate of the router is resting on, not up and down. A router will want to pull away from your grip. It will want to cut deeper into the stock or ride upon top of it depending on which way you move the router. The larger the bit or deeper the cut, the stronger this sideways force is. A firm grip is necessary. Perhaps read up on router safety basics in a woodworking magazine or talk to a local woodworker friend. Jun 21, 2022 at 17:48
  • 4
    Amazon isn't showing me the prices, but whatever your bit cost, return it. Pick your router first, then get bits that work with the router. Don't pigeon hole yourself into an odd-ball shank size (maybe 8mm is more common in UK/EU, but based on what you said, it doesn't sound like it), then trying to squeeze the wrong bits into it.
    – FreeMan
    Jun 21, 2022 at 22:48
  • 2
    To follow up on Triplefault's comment: Many routers also have the off/on switches located so that if it comes out of your hands, it remains on--spinning a sharp cutting bit at many thousands of revolutions per minute while the machine jumps around on your workbench, shop floor, or wherever you happen to be working. Practice on some "easy" cuts before jumping into anything "advanced"
    – gnicko
    Jun 22, 2022 at 0:02

2 Answers 2


The collet and shank size need to match. They aren't adjustable like a drill chuck. There's a little bit of wiggle room in the collets, but not enough for it to securely hold the wrong size shaft.

Imperial sizes (1/2", 1/4") are just about all you can find in US and Canada. Metric sizes (I think 6mm, 8mm and 12mm are the standard ones) are far more common in Europe and Asia.

Since all the cheap router bits come from China, they've got a much better selection of metric stuff than imperial, though you usually can still find imperial sizes. Sometimes listed in metric (6.35mm is very common to see).

You can buy more collets for most routers though, either from the manufacturer or third parties. For example (not recommending these people, just first on google search), this site sells all common metric and imperial sizes for dewalt routers, so you can use any bit you want.

  • 8
    I'm tempted to down vote the suggestion that mixing collet sizes can work - 1/2" and 12mm (or 1/4" and 6mm) are not "close enough" for a bit spinning at 20,000 RPM. The diameters are 5.8% different, which is an order of magnitude more than any manufacturing tolerances in bit shank sizes
    – Eli Iser
    Jun 21, 2022 at 14:41
  • 6
    @EliIser I certainly don't recommend doing so. But it does work in a pinch. Particularly if using the larger shank size in a smaller collet. But it'll be far safer to use the correct collet for the job. I'll take that line out anyways, it's a bad suggestion.
    – Grant
    Jun 21, 2022 at 14:43
  • 7
    What may work in a pinch may also cause a very sharp, rapidly spinning hunk of metal to fly off in a random direction, including directly at the tool's operator. I would strongly recommend AGAINST using a 6mm bit in a 1/4" collet or vice-versa. If your router has a replaceable collet then get the right size collet. If it does not, then get the right size shank!
    – FreeMan
    Jun 21, 2022 at 17:23

Router collets must match the bit size. So an 8mm bit must be placed in an 8mm collet.

As you have noticed, most routers have 1/4" or 1/2" collets. You have 3 options:

  1. Buy a router that comes with an 8mm collet. If this is the only collet it comes with, you will be limited in the future to only 8mm router bits. If it comes with multiple collets you should be future proof.
  2. Buy a router with a 1/2" collet and get a collet reducer from 1/2" to 8mm. These are fairly common and inexpensive.
  3. Replace the router bit with one that comes with a 1/4" or 1/2" shank. The slotting bit you linked is by no way unique and I am sure you can find one close enough with a more common shank size. If not, use one of the first two suggestions.
  • Thanks. I couldn't find a 3mm slotting with an imperial shank, only 3.2mm. Which might be close enough, but maybe the trim would work loose, I'd only know by trying and it feels like a very annoying mistake to make!
    – Codemonkey
    Jun 21, 2022 at 14:44
  • 1
    Yes, 3.2mm is 1/8" which would make more sense in Imperial measurements. If you strictly need 3mm than the first two options are still valid.
    – Eli Iser
    Jun 21, 2022 at 14:45
  • 2
    I agree with the idea of buying a 1/2" collet router and then using reducers for smaller-shanked bits. 1/2" routers are usually more expensive, but much more robust, versatile, and generally less prone to vibration, meaning they give better results. I'd also highly recommend a variable speed model... winged bits like the one you bought should ideally be run at slower speeds.
    – joe
    Jun 21, 2022 at 14:53
  • A good router will come with more than one collet to begin with, no need to buy an extra reducer.
    – MikeB
    Jun 22, 2022 at 15:14

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.