Hi there. "Wrong" doesn't mean that you didn't order the part Kal spec'd . . . it just means that the cord grip you have doesn't fit or won't work with your specific application.
Easiest solution would be ordering a new cord grip from McMaster-Carr: what size NPT ports do you have on your box from Lowes? what's the outside diameter of your cord?
With that info in hand, you should be able to find one that works: http://www.mcmaster.com/#standard-cord-grips/=kylubj
If you're not wed to having an aluminum grip, take a look at the "Nylon Liquid-Tight Cord Grip" models: same or better certs, nearly as good temp rating, water-tight, and half the cost.