This is my hand chuck, very handy for hand drilling, or deburring for instance.
It is a 10mm chuck, with an SDS adaptator shaft.
The handle is woodturned out of beech, and there is a set screw to hold the handle on the shaft.
The screw just goes into one of the flutes of the SDS shaft.
It can be used to hold whatever you want, it can be a tool like a bit, but also the work piece, for instance when grinding a round piece of HSS ...