Plumbing Grade: These are the fittings that were designed solely for the purpose of plumbing drainage and sewer systems for homes and business dwellings. They perform their task admirably, for basic construction of PVC assemblies. They don’t look too pretty however, as they are usually marked with ink, barcodes or raised/embossed lettering on them, but they are cheap. You can find these at your local Home Depot, Lowes or other hardware store. They are usually made by Nibco (www.nibco.com).
Furniture Grade: Furniture grade fittings are where the magic happens; they are what make PVC the tinker-toy system that it can be. While you can get basic Tees and 3-Way fittings from your Home Depot and Lowes, furniture grade fittings expand upon the basic idea, and add 4-Way and 5-Way fittings, fancy end caps, hinge elements and even caster inserts to put wheels on your project. In my previous post I recommended a store online called Formufit (www.formufit.com), which sells practically all the fittings you need to make any type of structure. In fact, a lot of the tips I explain in this Instructable, I borrowed from their website. They are a PVC project builder’s playground.
Whichever fitting type you choose you can find most of what you need either at HD, Lowes or Formufit, or you can also check eBay.