Among the new products on the market is a corner brace, designed specifically for reinforcing inside corner joints when building or repairing drawers, cabinets, benches, chests and box-shaped structures of all kinds. This new style of corner brace fastens to and reinforces three surfaces at once. Made by Stanley Hardware, New Britain, Conn. 06060, this three-surface corner brace (CD996) is made of zinc-plated steel and priced at $1.06 for a package of two. Energy Saver

Although most people know that flourescent lights burn much less electricity than incandescent bulbs, use of flourescents has still been quite limited in homes and apartment because of the special fixtures needed and the limited places where conventional flourescents can be used. A new adapter has changed all this - it permits converting almost every table and floor lamp,and many other fixtures, to flourescent lighting.

Called the Killer Watt,and marketed by Johnson Industries of 2638 Lyates Ave, Los Angeles, Calif. 90040, this adapter unit screws into a standard lamp socket in place of a convertional incandescent bulb. Available with single or double circular flourescents, one above the other, the single unit sells for about $12 to $15, while the double sells for a little over $30. The 19-watt single incandescent bulb, resulting in a wattage saving of about two-thirds, and it will last for about 12,000 hours for the incandescent bulbs. New Book

Profusely illustrated with many full-color photographs, as well as many line drawings and sketches, "Furniture Finish & Refinishing," by the editors of Sunset Books (Late Publishing Co," Menlo Park, Calif., $2,450, is a clearly written 80-page book.

Devoted primarily to rejuvenating old wood pieces with currently available materials and simple techniques, the book contain a special section on identifying woods, including close-up color photographs of 20 popular furniture woods, showing the shading and grain pattern of each.

Other chapters are devoted to preparing and stripping old furniture, staining and filling blemishes, and choosing the best type of finish for each piece. There is also an interesting chapter on special decorating techniques - distressing, stencing, stripping - as well as a helpful glossary and a chapter on brushing and spraying techniques.