This part, printed in stainless steel, bolts onto a modified version of the stock Rohloff 16-tooth sprocket
The modification involves welding four short threaded rods (actually, bolts with the head cut off) onto the sprocket -- one in every fourth hole (see the images on the linked page). Also, the sprocket teeth needed to be filed down considerably.
This is for a retrofit of belt drive to my custom recumbent bike. I had a modified Strida 30-tooth pulley, but it had a rather complicated mount to the bolts. This is simpler, and gives me slightly higher gear inches.
The Rohloff sprockets mount to the Rohloff hub with a Rohloff-custom 6-start thread (like a double helix -- a sextuple helix, I guess). I've tried printing such threads, but the dimensional accuracy of the stainless steel process is not up to the task.