I got some of the snap-in DC jacks for a 1590a build and they seem smaller than the 1/2" hole regular DC jacks take, but larger than the 3/8" hole used for 1/4" jacks. Does 7/16" seem right??
here's the data sheet:
http://www.mouser.com/catalog/specsheets/KC-300872.pdf (http://www.mouser.com/catalog/specsheets/KC-300872.pdf)
7/16 works or even 13/32 for a tight fit
Josh