This sleeve allows you to use 2.35mm shank rotary tools in a 3.0mm micromotor collet. The 2.35mm shank of the bit fits into the sleeve and the sleeve then fits into the micromoto collet.
The overall length of the sleeve is 19mm.
The insertable length is 17mm.
This enables you to use the smaller shanks without the time consuming task of switching collets.