No, no, no, I am not an old "anti metric" curmudgeon by any means. However. . . . .
I have been using Porter Cable routers for years and years. They come with 1/4 and 1/2 inch collets. Over the years I added 1/8 and 3/8 collets. Sooo, with imperial collets one buys imperial tools. Simple as that.
Enter the chinese. I have been able to buy some 1/8 ball nose and regular bits. But bigger than that? Iffy. I have had really good luck with the chinese HSS bits. I cut mostly softwood and domestic hardwoods. Virtually no MDF, Plywood or abrasive exotics. So HSS works better than carbide for me, especially at the ridiculously low chinese prices. In my oh so humble opinion HSS produces a better cut in softwoods with less fuzzies.
Today I was looking at the great prices for 6mm bits on the big auction site. Thinking to myself, I wonder. . . . does anyone sell a 6mm collet for the PC routers? Indeed, they do! And 8mm, 10mm, 12mm too.
The point of this post is that if you are using a router for your spindle and you would like to be able to use some of the inexpensive chinese tooling available, shop around for a collet set. I had no idea that folks were making metric collets for the PC and a lot of other routers. It is NOT a good idea to use a .25 collet to try to hold a 6mm tool. It is not going to run even close to true not to mention springing the collet so that it never runs true with a 1/4 shank again. That "1/8" stuff I have been using is probably 3mm, but springing the collet about .005-.006 is not that big of a deal evidently. I highly doubt our chinese friends actually grind those cutter shanks to .125.
"If you see a good fight, get in it." Dr. Vernon Jones