Cheers guys!
At the moment those are turboshafts, but there aren't 6 - they are a changeover/hold area, as the position of the shaft changes as it goes down the tube... for one, in their mid core positions they'd have to be outside the hull, if they were extruded down to there! It was a close fit to get them in the narrow point!
The central shaft is a feature which runs down the whole length of the station. I envisage it as a Zero G cargo transportation tube, maybe with a few tractor arrays, or, if they can fit, capable of flying the Workbees down hehe. Basically something big enough to move large objects/machinery for repairs etc.