I use the interlocking grip. Should the left thumb be extended down shaft as much as possible or should it be slightly bent and therefore shorter?

I would say shorter, that will help get some pressure into the top 3 fiongers on the grip which you need to be able to control the club, especially at hte top of the swing.

See the Golf School article on Power in the Grip.
Thumb aft of the shaft. “Meaty” part of the left heel pad on top of the shaft.

Toolish,

MORAD trained teacher preferred a long thumb. I think as Homer said, it depends on individual wrist condition. It related to the “double-jointed thumb” issue brought out by PH.

Why not use a short thumb for control and long for the big ones. Or short tight swing and long sloppy swing. All the good players do.

They do not have one swing for all occasions. I was always shocked at how short the good players were until it was worth there while to smash it 30 yds sometimes 60 yds longer.

Humbling.

We should learn some of that.

I Love you….PH. Great one!

Why not use a short thumb for control and long for the big ones. Or short tight swing and long sloppy swing. All the good players do.

They do not have one swing for all occasions. I was always shocked at how short the good players were until it was worth there while to smash it 30 yds sometimes 60 yds longer.

Humbling.

We should learn some of that.

Dart you may have explained something there… i remember watching Tom Watson down at Aust Mast i think 96/97 and he was not that long until he got on the par 5’s and id say he was 50 yards longer…wondering how he did that