geckocycles,
If your lathe is kind of long, I would agree with the LeBlond user group. Can you tell if it is (or was) in contact with the two shafts? Which end is it on?
The much longer lathes had one of these latched onto each side of the apron (and as many as necessary according to length). Whenever the leeward side of apron would pass a predetermined mid-point, it would pass over a raised button in the side of the frame which would disengage that support from the carriage to let it remain there supporting the shafts. Upon returning toward the headstock, the apron would 'recollect' the support. If there was a supprt on the other side, it would do the same thing at some midway distance from the tailstock.
If that IS what it is, I don't know why you would only have one unless the apron's own width counts for adequate support while at one extreme end.
Dave