JEONHO LEE 5 Actually this is a product of "Jacob" chuck, not originally Proxxon made however it goes well with Proxxon BFW40/E ( for 220 volt region version ) Finally, I can use more larger diameter bits (such 6.35mm =1/4 inch up to 10mm ) over the 6mm shank limitation, for both milling and drilling.On the other note,It gave me a big smile because it is printed on the paper, in Chinese letter "Patent pending."Japanese jokes is awesome!!!