My Techno lc4896 has those slides built into the x axis and has about a 16mm diameter screw 7 ft long. The small plastic spacers slide in the same channel that the ballscrew lies in. I think that the lead is close to 5 mm a turn and with the right motors and controller, the axis can move at speeds over 800ipm! I bet that without those spacers the ballscrew would whip itself do death at much lower speeds.
http://www.glenspeymillworks.com Techno LC4896 - 2.2Kw Water Cooled Spindle | Moving Table Mill from Omis 3 CMM, 500Lb granite base | Epilog Legend 32 Laser Engraver