I recently redid the lines on my rack & pinion and when I was under it I noticed there was what looked like an open section with ball bearings and a nut on it, I knew that didn't seem right so I after going to various part stores and googling round I went to a junkyard and found an old rack and there was just a small metal "cap" that covers this apparently, it came off with a couple taps of a hammer and a flat screw driver and now I was wondering when I put this one on does it need a seal or anything similar or do I simply tap it back in and hope it stays? For a more precise description its a small slightly domed cap that goes directly on the bottom of the assembly and cylinder area that the steering wheel/column connects to and its a straight shot down to the road just behind the transmission pan. To me it looks almost like a dirt or debris collection cap or pit meant to be removed and cleaned, because when it was taken off the rack at the junkyard it was pretty nasty inside.

EDIT: I found a decent picture of a rack and did a crappy MSPaint showing exactly what I mean.