There were several hilts used for Luke in ROTJ one of which was an old Obi-Wan stunt saber from ANH which was repainted and used as a stunt for Luke.As far as I know there were two main hilts used for the stunt work and for costume and then the so-called "hero" saber which was machined and used only for the insert shot of Vader examining Luke's saber when he says "I see you have constructed a new lightsaber" which was added in post-production.