I have a set of full length sizing dies for my 7mm08. When the decapping pin is set the standard 3/16 below the base of the die the threaded portion of the rod on the top of the die is a good two inches. I was wondering why they leave so much extra rod

Standardizing of parts! roger

Makes sense the same rod could be used for 7mm mag or 7mm stw which would have a longer die. Sometimes it takes someone else to point out the obvious.

Not only a 7mm. There is a small diameter rod for 222, 223, and most pistols and a larger rod for 270, 7mm, 30 cal etc. There are caliber specific expander balls for the two rod sizes.

For decapping before case cleaning.