Pretty self explanatory, it's a vise to hold PCBs steady when you are soldering your components.
The ball joint design gives you a fair bit of movement to position your work where it is most comfortable.
The main drive screw has reverse threads on one side to make the jaws clamp your PCB right in the middle of the vise.
The base has a few square holes for magnets to keep it steady on your workbench.
The vise can hold PCBs with a maximum width of 10cm.
The STLs are oriented the way I printed them on my Ultimaker and they were printed without a raft or support for minimum cleanup. The grooves of the jaws do need a bit of cleaning unless you've got retraction working well (I haven't bothered with that yet) but other than that the pieces should come out pretty much clean.
Please note that the threads are quite tight (at least on my print) and will require a bit of convincing the first few times. Add a bit of water to them to keep the heat down and work the pieces back and forth untill they work smoothly. I made them tight to minimise the flex in the jaws as you tighten them on your PCB.
The "swivel" and "bracket" parts have guide holes for short pieces of 3mm filament to aid alignment when gluing them together. I undersized the holes so you'll have to drill them out a bit if you decide to use them.
The main drive screw needs to be fairly solid or it will become too brittle. I first printed it with a 3.5mm fill spacing and then promptly dropped it on the floor which caused it to break in two...
Update 120427: Added pcb_vise_v2-drive_screw_2parts_left and right which is simply the drivescrew split into two parts to help vertically challenged printers :)
Update 120428: Added pcb_vise_v2-Bracket_2parts_bracket_left and -right (sorry about the long names, they help me keep track of all the parts). There weren't a hole lot of room to add in any alignment helpers here but I hope you can manage without them.