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In which case the collet is 8mm and not 5/16in. Cutter shank sizes in Europe are 6, 8, 10 and 12mm with 6, 8 an 12mm being the most common. in the UK the sizes are 1/4in (6.35mm), 8mm and 1/2in (12.7mm) as opposed to the American sizes of 1/4in (6.35mm), 3/8in (9.53mm - getting rare) and 1/2in (12.7mm). What's the betting that the router in question was supplied with UK or European size collets and that someone has "helpfully" translated 8mm to "5/16in" for the USA market?

I'll bet you are right. Amana makes an 8mm to 1/4" collet reducer adapter, on ebay for under 8 bucks. That is a really thin wall, .825mm. It looks thicker in the picture.

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I'm surprised Moderators here don't have access to IP addresses, I was a Moderator on another site, and member's IP addresses always appeared under the users member name. but I'll say that the OP should get a 1/4" collet rather than bother with an unsafe, and very thin, bushing only a few thousandths thick!..

Where is he going to get a 1/4" collet for some brand X router? I see no problem with a thin adapter. It is under no stress. People shim shafts all the time and handle a lot more power. Of course if you can tell the OP where to get a 1/4" collet, that would be helpful. Amana, the people that make the adapter is a well established bit and router accessory company and I am sure they would not sell it if they thought it was hazardous.

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