The 2015+ Mustang studs are 14mm x 1.50. It's kind of a mixed bag though. The Eibach 90.4.25.010.3 spacers come with previous Mustang 1/2 x 20 studs and nuts to bolt onto your hubs. So you'll obviously need 14mm x 1.50 nuts to retain the stock metric studs. But the nuts that come with the Eibach spacers are not exactly like standard lug nuts. They're lower profile. I thought about mixing and matching like this on mine, but decided it was simpler just to replace the studs. It's not that hard.