I have always considered Acorn lug nuts to be the closed end type of lug nuts.
However, it seems that I have recently seen other descriptions, based on the shape of the lug nut.
I just don't want any surprises at inspection/tech.
I am using common (Summit), open end OEM replacement type lug nuts with tapered seats on steel wheels and OEM studs. (Record is 105 mph in my class).
Any clarification on the "Acorn" thing would help.
Steve.