[Mick]

12 golfers have won three legs of the career grand slam. We've already identified Stanford grad Tom Watson and Raymond Floyd.  Who are the other 10?  And a bonus question: which of the 12 finished second the most times at the Major that they failed to win?

Jim Barnes, pre-Masters. Won four majors, played in the inaugural Masters (1934) at the age of 48. Won two PGAs. No green jacket.
Tommy Armour (Sr.), same issue. won three majors, played first Masters at age 38. Best finish was tie for 8th.
Walter Hagen won 11 majors, didn't play in the Masters until he was 41.
Byron Nelson won five majors, only played in the British Open in 1937 (finished 5th) and 1955.
Sam Snead finished second four times at the U. S. Open, never won it. Almost won in 1939. He thought he needed birdie when par would have won it, so he ended with an 8.
Arnold Palmer never won the PGA Championship, finishing second in 1964, '69 and '70.
Lee Trevino won six majors, but never the Masters. Trevino cut his teeth in windy Texas, and had developed a low-fade game, when Augusta favors high draw golfers. 92 PGA tour wins, best finish at the Masters was 10th in 1975 and 1985.
Raymond Floyd and Tom Watson, noted.
Phil Mickelson wins the "almost" prize, having six runner-up finishes at the U. S. Open with no wins. He double bogied the last hole at Winged Foot in 2006, leading to a Geoff Ogilvy win.
Rory McIlroy needs a Masters win. He had a four-shot collapse at the 2011 Masters, that was the closest call.
Jordan Spieth hasn't won the PGA -- best finish was 2nd in 2015. He's still only 29, so there's still time.

[Mick]

12 golfers have won three legs of the career grand slam. We've already identified Stanford grad Tom Watson and Raymond Floyd.  Who are the other 10?  And a bonus question: which of the 12 finished second the most times at the Major that they failed to win?

Jim Barnes, pre-Masters. Won four majors, played in the inaugural Masters (1934) at the age of 48. Won two PGAs. No green jacket.
Tommy Armour (Sr.), same issue. won three majors, played first Masters at age 38. Best finish was tie for 8th.
Walter Hagen won 11 majors, didn't play in the Masters until he was 41.
Byron Nelson won five majors, only played in the British Open in 1937 (finished 5th) and 1955.
Sam Snead finished second four times at the U. S. Open, never won it. Almost won in 1939. He thought he needed birdie when par would have won it, so he ended with an 8.
Arnold Palmer never won the PGA Championship, finishing second in 1964, '69 and '70.
Lee Trevino won six majors, but never the Masters. Trevino cut his teeth in windy Texas, and had developed a low-fade game, when Augusta favors high draw golfers. 92 PGA tour wins, best finish at the Masters was 10th in 1975 and 1985.
Raymond Floyd and Tom Watson, noted.
Phil Mickelson wins the "almost" prize, having six runner-up finishes at the U. S. Open with no wins. He double bogied the last hole at Winged Foot in 2006, leading to a Geoff Ogilvy win.
Rory McIlroy needs a Masters win. He had a four-shot collapse at the 2011 Masters, that was the closest call.
Jordan Spieth hasn't won the PGA -- best finish was 2nd in 2015. He's still only 29, so there's still time.