Be careful if you buy if you buy cheapo ones from ebay, I bought some and the diameter was larger than the standard 3/32. Not really a problem if you use a keyed chuck handpiece, but infuriating if you have a quick fit one. I bought about 2 dozen and about a quarter of them also had dodgy threads in the screw hole - they didn't really bite properly and just rotated without tightening.
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