On every hole on every golf course on the planet, there's a flagstick. That flagstick indicates where the golf hole is. Lots of golfers know they're trying to put a 1.68-inch ball into a 4.25-inch cup. But do they know the golf flagstick height?
The USGA recommends a golf flagstick height should be at least 7 feet tall, measured from the bottom of the flagstick in the ground to the top of the stick. That means the visible portion of the flagstick isn't 7 feet, but it's more like 6 feet, 8 inches.
However, the golf flagstick height the USGA recommends doesn't mean every flagstick is 7 feet tall. As many golfers have experienced, there are golf flagsticks closer to 9 or 10 feet in height. These flagsticks are used when a golfer has difficulty seeing the flagstick from their approach shot, so courses will use taller flagsticks with the idea of giving golfers a better sense of the hole and an aiming point.
Courses choose the flagstick as they wish, and they can be made of whatever material the owners would like: wood, metal, fiberglass, plastic. You name it. The material isn't relevant so long as it can hold some kind of marker on top -- it doesn't even have to be a flag, with Merion using baskets, for example -- to make clear the stick's location. It also has to be straight and indicating the center of the cup.
The rules around having a flagstick in the hole during a putt made on the putting green will change in 2019, with the USGA and R&A taking away the penalty for hitting the flagstick while it's in the cup with the ball as a result of a putt.