6.25mm (1/4" HEX) male to 3.95mm female bit adapter
I wanted to use bits from a mobile phone repair toolset in my "Bosch GO 3 601 JH2 020" which uses standard 1/4" HEX sized bits.
The size of the interior hexagon gap gives a clearance of 0.35mm to 0.4mm, sufficient space to allow the smaller bit to slide in without much resistance.