It's called Stetro, a little plastic glob that slips around the shaft of a pencil, and it is the best thing that's happened to handwriting since the teaching of penmanship died in the schoolroom. With Stetro in place, fingers fall naturally into indentations that make it easier and more comfortable for many youngsters to hold a pencil. Since Stetro hit the market last summer, 516,000 of the 39-cent pencil grippers have been sold. Its creator, Chris Rusk, 28, hopes to sell as many as 10 million in 1986—and all that without market research or advertising.

Stetro was born about three years ago on the kitchen table of the Rusk home in Crawfordsville, Ind. Rusk's wife, Susie, was baking chocolate-chip cookies, and Chris was giving his 5-year-old son, Troy, a printing lesson. "He held the pencil like a steak knife," Chris recalls. Troy's dad molded a hunk of cookie dough around the pencil to give the lad a proper grip. It helped.

Rusk next made plastic versions of his Stetro (named for his children, Stephanie, 5, and Troy, now 9) and tested them on neighborhood children. Encouraged by their response, Rusk took a second mortgage on the house and borrowed from his family to sink $20,000 into his invention. He got a patent, rented a one-room office and quit his construction job. "Everyone told me I was nuts," he says.

With lists culled from library directories, he mailed 35,000 fliers to schools and educational supply houses. Soon orders poured into his Rusko Writing Company. Now, Stetros are rolling off the production line at a plastics platit in Noblesville. lnd. Made of FDA-approved plastic, a Stetro is harmless even if accidentally swallowed. Rusk should know. "I ate the first one," he says, "just to make sure it wouldn't hurt anybody."