I bought a set of these (SK 10?) used on online auction site, and was surprised when I received them how tiny and lightweight they are. They seem good and tight, but I'm still wondering if they're not meant for something much more lightweight than my intended purpose -a horizontal y axis for a woodwoking router (fixed gantry,moving table) with 15" travel on 26" long rails. They did come with 4 trucks on each rail. Will they work for me? Should I use more than 2 trucks/rail? (I was hoping I might be able to sell the extra trucks). The bolts that will fit their tapped holes are really small! Thanks!