48 springs, sized perfectly for zero friction addition when used to add power pickup on 2.0mm axles (OO and HO standard size). They are a delight to use. Simply remove one wheel, add the spring and replace the wheel-set, making sure you note which wheel is ‘live’ to the track. Drill a small hole in the floor of the coach/tender/caboose etc, and solder a bit of fine wire to the tag end on the spring. Connect the wire to your flickerfree or loco pickups etc. They will add nothing to the drag at all and will always be able to give perfect pickup as long as you keep track and wheels reasonably clean.