DISCONTINUED: The LiftMaster/Chamberlain 41C4677 complete screw-drive trolley assembly [041C4677] is no longer available from the manufacturer. The 41C5141 square-rail trolleys fit chain/belt rails, not screw drives, so they are NOT substitutes.
Aftermarket versions of this trolley still surface from time to time — call us at (866) 965-5599 and we will check current availability and pricing for your opener.
About the Original 41C4677 Screw Drive Trolley (For Reference)
Complete trolley assembly