[Scottluther]

I just want a little reassurance, don't want any magic smoke.
I'm wiring the gecko 251x to the smoothstepper's bob and terminal 12 is listed as Common, yet says to connect to the bob's ground. I thought Common always referred to the 5v not ground. And in reading the "zone", I am still confused.

First, should terminal 12 on the 251x be connected to a gnd on the bob?
Second, is terminal 12 5v or a gnd?
Third, is it a grd wire for the step and direction signals?

[UUU]

Terminal 12 is the ground reference for the step, direction and disable terminals. It's terminals 9 and 10 that will have 5V or 0V states relative to 12.

So yes, this will be wired to the bob. I don't have the same bob as you so can't advise exactly which terminal on that - mine has connections for both "5V common" and "Ground common" setups - so I'm using the "Ground common" one.