Aloris #6 Toolholder Q- What's This Bolt For?

I don't really feel like as much of a beginner these days, but no expert either, hah hah! But this sounds to me like a beginner question.

I have a DTM QCTP and just acquired a #6 holder, same as an Aloris #6. So---- WHAT is this bolt that goes up from the bottom and is ground flush with the top, and is visible in the tool holding area?

Also curious what most folks are doing with a holder like this- is it meant for more than one tool at a time?

Thanks!

Bernie...

Aloris #6 Toolholder Q- What's This Bolt For?