Assuming the broken club is a driver, the area on the shaft just above the hosel impacts at a teed up ball rather than the club face. The stationary weight of a Golf ball is sufficient to strain the tensile strength of a graphite shaft. With a club head attached at the very end of the club, it further increases the momentum of a downswing. This is mostly caused by addressing the ball too close to the body and an incorrect swing plane going back. For an iron, a breakage could be mainly caused by hitting the toe of the club into a relatively hard surface in the down swing. This usually happens to a graphite shafted game improvement iron. The reason being that game improvement irons have larger and wider club face area, in which when it is swung at a particular speed with only its toe part hitting the surface, the tensile strength of the shaft at the hosel is at its most vulnerable. This is mostly caused by the use of a non-custom fitted iron where certain compensations (maybe due to shaft length and body height not ideal) in a swing occur. Also may be caused by incorrect swing plane.
Hosel is the the socket (or neck) in the head of a golf club into which the shaft is inserted.
hosel
What is the hosel size for Ben Hogan bh5 golf clubs? irons
El hosel
The Hosel (one 's') is the socket or neck in the head of a golf club into which the shaft is inserted.
the serial number is stamped on the hosel of the driver (hard to find, but its there), the serial number for the irons set can be found on the hosel of the 6 iron.
Shank
The socket is known as the hosel, it is where the head is connected to the shaft.
This is the width of the bottom of the shaft, where it enters the hosel.
You could, but I wouldn't recommend it. You could use a belt sander to sand it down slightly, but not too much so you'd ruin it. You would honestly be better buying the proper shaft for the hosel.
Generally .370 for irons and .335 for woods these days.
ho·seln.The socket or neck in the head of a golf club into which the shaft is inserted.Above retrieved from Answers.comViper1