These are used to plug the center of the golf shaft in bore through golf club designs like the older Callaway bore through woods and irons and older Titleist drivers. In a bore through where the shaft goes through the bottom of the clubhead the hole in the center of the shaft needs to be filled. That is what these pins are for. The smaller tapered pin for graphite shaft and the larger pin for steel shafts.
Here is a couple of links from Callaway's web site and you can see where the shaft comes through the bottom of the sole and the pin is used to plug the hole in the center of the shaft.
Here is a link to a You Tube video on how to finish the sole on a bore through driver.
Date published: 2016-11-23