Disclosed are devices and a system for compensating for thermal expansion and contraction of rail mounted solar panel rooftop systems. In one aspect, a floating end clamp that secures a solar panel in slidable captive cooperation with a mounting rail. In another aspect, a rail splice bridges two mounting rails with a gap between the rails for thermal expansion and contraction. The rail splice includes indicia for setting the gap distance between rails based on ambient temperature at the time of installation. In another aspect, a spacing gauge includes indicia for setting the gap distance between rails based on ambient temperature at the time of installation.