Go into some furniture stores. Every furniture maker should do this frequently. The upper end from manufacturers like Hendredon, Baker, Ethan Allen, Drexel will all use center mounted wood slides. This keeps the drawer centered, stops it from racking side to side and keeps it from running on the drawer sides only. They also provide additional support for wider drawers. Go into Bob's discount, Walmart and other lower end furniture stores and the drawers will be on metal slides. If you have the skills to build an heirloom, enough said.