The YM's come in three sizes: 29 - 35 (measured: 34,3 mm) and 40 MM.
YM's in 29 mm (Ladies) and 35 mm ("Midsize") come with the Cal. 2235 movts. (often referred to as one of the best Rolex movts. ever made). The Ladies and midsized YM's have a
TWINlock winding crown unlike the men's sized YM that comes with a
TRIPlock winding crown.
Like the bezel (unidirectional, btw.), the
dials of the SS/PL YM's is made of Platinum 950, too. The back of the dials says "PT 950" (
Source).
Like the Sub Date "LV", the dials of the YM's have "semi maxi hands" since only the MINUTE hand is maxi whereas the hour hand is standard sized. The GMT IIc's, however, have FULL Maxi Dials.
The YM's come with a solid centre link bracelet, but the clasp is still of the "bent sheet steel blades" type.
The YM's in TT with a white dial have a special kind of lume construction. The black indices don't glow, but small triangle markers - barely visisible to the naked eye in normal lighting - will glow at night:
(Source unknown; pics from my Photobucket).