When you want to machine a workpiece (by milling, drilling, engraving or else) you need a what we call machining unit (BAE), which is fixed to the Z-table of your CNC-machine.
The BAE consists mainly of a power driven spindle. For the tools (milling cutter, drill, engraving tool, etc.) you need a collet which is available in different diameters.
Around the spindle you need some parts like holder, extraction adapter - with or without plate brush, electric connection and its integration in an emergency stop system, to meet the safety instructions.
The following overview shows the machining units available together with KOSY: