Roll-N-Lock 17-19 Ford F-250/F-350 Super Duty SB 80-9/16in M-Series Retractable Tonneau CoverRoll N Lock(R) M Series(TM)the most advanced retractable truck bed cover made, has redefined the rules for truck bed security. From its retractable function, which permits opening or closing in literally seconds, to its rigid, vinyl over aluminum laminated construction, this hybrid cover offers everything other covers do not. There are no snaps to manipulate, there is no roll or bundle to lash down or stow, no cross bars to negotiate, no fabric