The screw kit depends on if the holes in the floor of your airplane have been carefully removed and are close to new size or if they have been enlarged by unskilled rivet removal or the rails have been changed before. It will make a difference if the previous rails installed were Cessna rails with predrilled holes in the rail. (They do not normally line up well and the floor has been mis-drilled some to force them to align). If the holes are good, use the SR6-SCREW-KT kit. If the holes are enlarged some, use the SR8-SCREW-KT kit.