Popular stem in the mid to late 80's.  More 'Aero' in design than the earlier 1A and similar designs.  Both the conical expander and this wedge style expander types were produced.  Exact date ranges for each are unknown, but since it's a hidden part of the stem anyways, there's no real reason to fret over one version or the other.  What you will want to look out for is that some of these later wedge style were meant for 26.0 diameter bars instead of the older 26.4mm Cinelli standard.