What do drawer-slide weight ratings mean?

I need to order some drawer slides for a shop cabinet I'm building. There's a pretty big price difference between the various types, and what's the deal with weight ratings? How do I determine which ones to use?
—Frank Headley, Millville, N.J.

Choosing the right hardware is one of the most important parts of any project, Frank, especially when you're talking about load-bearing hardware, such as hinges or drawer slides. Most manufacturers classify their drawer slides as light-, medium-, or heavy-duty. These serve as general guidelines to help you select the slides that best match the intended use. For example, you'll often find light-duty slides on drawers in bathroom vanities, while kitchen cabinets may use light-duty or medium-duty slides, depending on the size and intended purpose of the drawer. For most of the shop projects featured in WOOD®, we use heavy-duty slides.

In addition to these general classifications, manufacturers also provide specific weight ratings. (If the retailer where you purchase your slides doesn't have this information, contact the manufacturer or check their website.) These ratings indicate how much weight a pair of slides can safely
support through a given number of open-and-close cycles of the drawer (usually 50,000–75,000 cycles). In other words, a pair of drawer slides with a rating of 75 lbs. is able to carry that much weight throughout its intended life span without failing.

If you're unsure about which general classification of drawer slide to use on your project, go by the actual weight rating. Keep a couple of things in mind as you plan your project, though. First, include the weight of the drawer, as well as the contents, when calculating the weight load. And second, manufacturers base the load ratings on the assumption that the slides are securely attached to a well-constructed drawer and cabinet. Particleboard and MDF don't hold screws very well, so stick with plywood or solid wood for best results. If you follow these guidelines, your drawers should operate trouble-free for years.