1) Anything! There's steel, brass, spewter... anything
2) Steel is generally brighter, thin sounding, resonants well. Brass is warmer, rounder, not quite as thin sounding as steel, resonants well, pricy. Spewter (Ibanez edge) has a dulled treble reponse, more mids and bass, pseudo "warmth" and thickness, cheap. SOmething like so...
Ping manufactured OFR has brass trem block. From the pic, it looks better made than those schaller manufactured OFRs... the saddles are seated well, and the chrome is even.
IMO, go for the Gotoh Floyd Rose still.
Cheaper and tops the OFR anyday.