The ones you have are on the left.The ones you need are similar to the ones on the right.
Z31 wheels have no 60degree conical taper for the lug nut at far left to fit. The lugs on the right use a washer in between the nut and wheel, and the cylindrical or 'shank' part of the lug nut goes into the wheel.This was common for most all old mag wheels. Nowdays a handful of automakers use this syle for OEM. Toyota / Lexus, Jaguar, Lincoln LS has them, Mitsubishi has some.
http://www.mcgard.com/custserv...shank