As many people do, you probably buy sandpaper using the eyeball method -- how it looks (fine, medium, coarse, etc.). Today, you'll learn to choose the grit that sands things or smoothes, just as the pros do -- by the numbers. The numbers on the back of the sandpaper indicate the size of the particles on the face. Sixty-grit means the particles passed through a screen with 60 openings per inch; thus, the lower the number the bigger the grit. Thirty-60 handles heavy sanding, 100-150 is medium, and 220 is for finish sanding. Also indicated is the type of grit: garnet (which looks like sand, thus the name) is most common and most economical. There are also newer synthetic abrasives such as aluminum oxide and silicone carbide, which are more durable and more expensive. And if it says "open coat," it has fewer particles and won't clog up as fast or easily as a closed coat. Naturally, this all depends on the type of wood and whether the sanding is done by hand or with a power sander. And that's the On The House tip for today.