Collets with diameters of 6.0, 6.35, and 8 mm for a router

I have a couple of small trim routers, and a link to collets for them came up in the comments one day—not just the standard 6.35 mm size, but two additional sizes, 6 and 8 mm. I thought, why not order them? They might come in handy.

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I’m talking about these routers, the corded one and the cordless one, as well as some rather interesting extended collets. Those would definitely require drilling out the spindle, with precise centering.

At first, I only wanted to order the 6 mm collet. Then I thought, well, the 6.35 mm one might come in handy too, just in case. And when I found out that buying all three as a set cost almost the same as ordering them individually, I ordered the whole set.
I can also recommend a couple of individual listings with lots of sales — one, two.

Some time later, I picked up a combined parcel from the post office, and inside was the little envelope with the collets. But the label surprised me: it said Germany...


As promised, they sent three collets in three different sizes.


The collet dimensions from the product page, in quite a bit of detail.


And here I decided to measure them myself, just to be on the safe side.
First, the 6 mm one.


Next, the 6.35 mm one. Since its dimensions mostly match the previous collet, here are the measurements in abbreviated form.
Yes, the 6 and 8 mm collets are metric, while this one is imperial, for a 1/4-inch shank. Bits with that shank size are almost impossible to find in local stores, which is exactly why I ordered a 6 mm collet.


I wasn’t really surprised by the 6 and 6.35 mm collets, but I was quite surprised to find that an 8 mm shank bit could be fitted into a router chuck designed for 6/6.35 mm.
This collet is noticeably different. For one thing, it’s shorter; also, at its narrowest point it tapers almost to nothing, unlike the previous two.


While inspecting and measuring them, I noticed a couple of things:
1. The smallest collet has a slit and a notch on the opposite side. The 6.35 mm collets (both the new one and the original) don’t have this.
2. The inside surface doesn’t seem to have been finished. It’s hard to see in the photo, but I’d have liked it to be neater, since this affects runout.


Here’s a comparison with the original 6.35 mm collet. There’s a slight visual difference, but that’s mostly because I’ve already used the original collet, so its black finish (if that’s what it was) has partly worn off.
Otherwise, it’s almost identical to the new 6.35 mm collet.


I decided to check how well the collets hold the tooling. First, the 6 mm one. It fits just like the original, and I didn’t notice any difference in that respect.


I couldn’t find any bits with this shank at home, so I just grabbed a 6 mm drill bit. At first, it seemed to have a little runout.
It tightens almost to the maximum torque, with very little margin left, though that’s subjective.

I took the drill bit out and thought the runout might be caused by the markings stamped on the shank. I measured where the collet grips it and found that the markings couldn’t be the cause, since they’re much deeper. I tightened it again and didn’t notice any runout. Either there wasn’t any to begin with, or it just seated better the second time.


The 6.35 mm collet fitted just like the original. It grips very well, I couldn’t detect any runout, and there’s some tightening force to spare.


The 8 mm collet has a few issues, so I haven’t tried it yet. First, I don’t have any bits with that shank size. Second, the hole in the spindle needs to be drilled out, and third, the hole in the collet nut needs to be drilled out too.

I can say that after drilling it out, it should be able to grip 8 mm shanks just fine. But I’m not sure I need that at all; the 6.35 mm bits are enough for now. The only thing I’m unsure about is whether it will grip securely, since the collet itself is shorter.


My conclusions will be mostly subjective. Overall, not bad. All three collets fit properly, and they grip 6 and 6.35 mm bits, but how long they’ll keep doing that is a big question. I bought them mostly as spares for when the original one dies, and in case I need to buy 6 mm bits locally.
As for the 8 mm collet, I think that’s a pretty questionable idea. It’s shorter and requires drilling out the spindle and nut. Is it worth it? I’m not sure. But since it’s basically a “bonus” collet, I’ll keep it—might come in handy.
The one thing I definitely have complaints about is the finish on the inside bore. The slight wobble I got when I first tried clamping a 6 mm drill bit was probably caused by that.

In short, you can buy them for the money. I wouldn’t call them good, but they don’t seem outright bad either.

That’s all for now. I hope this was useful.