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?
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