Four years ago, new partners William Biesemeyer and Roger Thompson took a look at their 5,000-square-foot storage facility and asked each other, "How are we ever going to fill this up?" Today, Biesemeyer Manufacturing Corp., of Mesa, Ariz., fills half of its new 80,000-square-foot building, and at the rate the former mom-and-pop cabinetry shop is growing, the tenants using the other half shouldn't count on too long a stay.

The $299 (retail) gadget that is likely to evict them has transformed a sole proprietorship shipping a ton-and-a-half of merchandise a month into a $1.8-million-a-year (1983 sales), 42-person corporation unloading about five and a half tons of hardware a day. It is the Biesemeyer T-Square Saw Fence System. Acclaimed by an international trade fair as the greatest contribution to the wood-working industry for 1980-82, Biesemeyer's invention unites the common draftsman's T-square with a hairline pointer, built-in tape, and lock mechanism, creating an adjustable guidance system that converts any table saw to a precision cutting tool.

Biesemeyer claims he was hunting neither fortune nor glory when he designed the saw fence; after 30 years as a woodworker, he was simply fed up with having to use table-saw guides that were unwieldy and inaccurate. "I said to myself, this is just not right. There has to be a better way." Having found it, however, Biesemeyer realized he had no idea of how to get the product to market. "I could never sell worth a darn," he admits.

Enter Roger Thompson, then a marketing executive with Fotomat Corp. "After one conversation," says Biesemeyer, "I knew this was the man the company needed more than anything in the world." The admiration was, and remains, mutual: Thompson owns 49% of the business, yet he feels no need to have his own name on the company. Why not? "Bill's designs are the best," explains Thompson, "and they always have been. The name Biesemeyer is synonymous with quality."

The name Biesemeyer was also synonymous, once upon a time, with high-performance pleasure boats as well. A decade ago, "I own a Biesemeyer" was a boast made not by power-tool operators but by powerboaters, and the Biesemeyer Boat, designed by Bill and his brother Rusty, won wide acclaim for its clean lines and speed specs. With no management or marketing expertise between them, however, the Biesemeyer brothers took their swift little boat company and ran it aground.

With Thompson as skipper, however, Biesmeyer is convinced the new company will sail. Thompson himself hawks Biesemeyer's elegant invention to some 10 trade shows a year, aided by the kind of sophisticated display equipment that Biesemeyer used to envy from afar.

But it is not the glitz that sells the saw fence system, Thompson says. It is the simplicity. "People come up at a show and their first reaction it, It's so obvious. Why didn't anybody think of it before?"