What is the most difficult “hole-in-one” on the PGA Tour? Please limit your responses to holes where at least one hole-in-one has been made by a professional golfer during the Tour.
Why make that limit? If there is a par 3 on the Tour that hasn’t been holed-in-one, that would seem to make such a hole, pretty much ipso facto the most difficult “hole-in-one on the PGA Tour”. 
I don’t know why you restrict it to par threes. Holes in one have been made on par fours. It was only once during a tournament though.
Well, in fairness, some par 4s can be conceived of as holeable, but ALL par 3s should be holeable, pretty much by definition. So if a par 4 hasn’t been holed out in one, that doesn’t make it the hardest “hole-in-one” on the Tour, except in the same sense that all par 5s are equally the “hardest” to do that on. But if a par 3 hasn’t been holed out, that means that something that could be expected to happen hasn’t.
Because that is the limit I made? At least with the holes where it has happened we know that it is possible, whereas with all the others we don’t know yet.
It seems to me that getting a hole-in-one also has a certain amount of luck involved in it. Yes, a skilled golfer will know where to hit his first shot on a par 3 in order to get it close to the hole, as well as having the ability to actually put the ball in that spot, but beyond that, it’s often a matter of a lucky bounce or roll.
My mother is by no means a great golfer, but she’s hit two aces in her life. When I asked her about how she got the first one, she said, “I hit the ball, and it just rolled in.” In other words, she didn’t do anything any differently than she would have normally…she just benefited from a fortuitous roll.
Also, even within one hole, the pin placement on the green varies by day within a tournament, and some placements may be more likely to lend themselves to an ace then others.
if there’s a par 3 on a course that’s in the regular PGA rotation that’s never been aced during the PGA’s tournament there, I suspect it’s more a matter of random chance (and relatively small sample size), versus there something about the structure of that hole making it particularly “hard” to ace.
For example, the “island green” 17th hole at TPC Sawgrass in Florida (home of The Players Championship tournament) is seen as an intimidating hole by players, because of having no margin for error – and, yet, eight aces have been hit there during the TPC.
The way I’m reading the OP, the question is about what is the most difficult hole-in-one a golfer has ever made on the PGA Tour. There may be holes that are physically impossible to make or so improbable they may as well be, and those wouldn’t be as interesting.
This is what I was hoping for by reading this thread.
Me, too.
That was on a hole, the 332 yd par-4, 17th at Phoenix, that the pros usually can drive if they want to. That Magee’s tee shot went in as a carom off the putter of Tom Bynum, who was in the group (or two) ahead, and thinking about his putt, is even funnier.
This drive was on the 433 yd par-4 12th at Kapalua. And missed going in by about three inches. https://twitter.com/PGATOUR/status/950291091349151744/video/1
My first thought was of the 16th at Cypress Point. The pros don’t play there anymore because of the club’s membership policy, but when they did, as part of the Clambake/AT&T Pebble Beach Pro-Am, it played as a 230 ish par 3. It’s listed officially as 219, but the carry was often more than that. Oh, and it’s often into the wind. Nonetheless, Jerry Pate aced it in 1982. Decent view of a typical tee shot here: Cypress Point Still Has Presence (Unofficially) At Golf's Pebble Beach Pro-Am
I’m sure there are par-3s on Tour that haven’t been aced. Be a bit of a research project to find them though.
So, what you are asking is what hole-in-one that has occurred was the hardest to accomplish, not what hole on the Tour is the hardest to hole in one shot. Got it.