Thoughts on this lead screw
http://www.mcmaster.com/#6642k11/=vtockj
comes in 18" lengths

and either these nuts
http://www.mcmaster.com/#6642k31/=vtoeev

or these nuts
http://www.mcmaster.com/#6642k21/=vtoexq

Each rotation is 1/41.7" = .02398" = .609mm