Coming to the 15th green in the final round of his 28th Masters tournament in Augusta, Ga., Jack Nicklaus stood four strokes behind the leader. At the age of 46, with his last Masters victory 11 years behind him, Nicklaus seemed an unlikely winner. But the Golden Bear had a secret weapon: a putter with an oversize blade that looked to sportswriters "as big as a hockey stick." Manufactured by Nicklaus' own MacGregor Golf Company and dubbed the Response ZT, the aluminum, lead and brass putter has a six-inch-long head one-third larger than normal size. It had already helped Nicklaus to birdies at the 11th and 13th holes. Now, as the gallery erupted with applause, Jack took his giant killer and in sequence sank an eagle (at 15) and two birdies. After holing out with par on the 18th to win a record sixth Masters title, he said, "The putter did the work."

The next day MacGregor's phones started ringing. By noon the company had sold 5,000 Response ZTs. Since then orders for more than 50,000 (at $62 each) have come in. The club's weight is distributed in the heel and toe to compensate for the force of balls hit off-center, eliminating the effect of torque. Hence ZT, for "zero twist." "The first time Jack looked at the ZT," laughs Clay Long, 34, the MacGregor R and D director who designed the out-size putter, "we felt like we had to put on big clown shoes." But the big blade's stroke was no joke. "The more I fiddled with it," says Nicklaus, "the more I liked it. Most players, including myself, have a tendency to pull up. The larger putter eliminates that. It has more inertia and a larger sweet spot."

Since Nicklaus' Masters performance, other pros have begun to use his putter. Recently Denis Watson borrowed Nicklaus' backup ZT and finished eight strokes better than his previous round. Says Jack: "I don't think I'm going to get it back."