CHICAGO (AP) _ An amateur tennis buff says he wasn't looking for money or success when he came up with a design for a tennis racket filled with fluid. Just relief.

''I had a bad case of tennis elbow for about six months,'' Marvin Sassler of Wayne, N.J., said Wednesday as he displayed his ''hydraulic racket'' at the annual National Design Engineers Show.

''So it occurred to me that if I put a movable mass at the head of the racket, I could cut way down on the vibrations that cause muscle injuries,'' said Sassler, whose Dynaspot Corp. is producing the racket.

The electrical engineer and a designer was one of more than 780 from nine countries touting their creations at the show this week at McCormick Place convention center. Other novelties on display included:

- A radio headset made of a special plastic that can be rolled up into a ball in the palm of the hand

- Special clothing made and fitted by computer, without stitches.

- Ceramic golf clubs, offering a harder striking surface.

- Plastic shoes for cyclers with a clip on the sole that attaches to the pedal and makes the sport less tiring.

- A type of steel that won't clang when struck by a hard object. Its designers say the noise is dampened inside the metal.

Then there's a tea kettle that's made with a special plastic so it's always cool to the touch, even when water is heated inside. The kettle, being introduced in U.S. markets, is a popular item in Europe, said spokeswoman Lillie DeShields for DuPont, which invented the plastic.

''Americans just don't like new things. We're trying to get (the U.S. version) to look like metal so people believe us when we say it won't melt,'' Ms. DeShields said.

The winners, chosen from thousands of entries as the best technical ideas of the year, must also offer ''high consumer interest,'' said spokesman Lars Soderholm for the Des Plaines-based publisher, Cahners Publishing Co.

To be eligible, an invention ''first has to be real,'' he said, noting that editors judging the competition must study working models.

''We get a lot of figments of the imagination, ideas on paper that may or may not work,'' Soderholm said.

Sassler wasn't the only athlete to score. Another winning design came from ''a golfer-type, you know, an entrepreneur who got a good idea and ran with it,'' Soderholm said.

The result? A glow-in-the-dark golf ball to make twilight rounds more than a frustrating series of swings in the dark.

The translucent ball lights up with a luminescent chemical stick, inserted into its core. The stick gives the ball an intense green glow that lasts for four to eight hours. The ball sells for $4; the sticks for $1 each.

Other winners include the ''Med Module,'' a plastic desk console that provides blood pressure, pulse and other medical readings. The console was developed by General Computer Corp. of Dunedin, Fla., said Bill Griffiths, coordinator for the project.

The module is being tested at 3,200 pharmacies nationwide and is made available to customers who purchase a $6 membership card, with results of the screenings stored by the computer for future reference, Griffiths said.

The show, in its 34th year, is sponsored by the American Society of Mechanical Engineers. It is not open to the public, but was expected to draw about 30,000 exhibitors and others, said spokesman Jim Greif.