According to the product description, it fits a 5/8" mount and converts 5/8" grinder mount to M10 thread. The description on the Packaging is the same. In fact, an adapter was included in the packaging that does the exact opposite - converts the M10 mandrel to a 5/8" thread. Useless for the M10 tapping chuck I have on my 5/8" "-want to attach a sander. In fact, the drill chuck I also bought was paired with this adapter on the same listing. Would give zero stars if that was an option. get a refund.