300zx front calipers

[sr2092]

How can you tell if you 26mm brakes or 30mm brake calipers?

[soloknoxdrftr]

refers to the thickness of the rotor...take a mic and mic the width of the opening in the caliper, I'm sure it won't be exactly either of the measurements but should be somewhere close.

[Drifting Kalamari]

Measure the groove where the rotor would go, it should be about ~35mm; the 26mm caliper has a ~30mm groove where the rotor would go.
26mm is only aluminum, and both 26 & 30mm Aluminum calipers have heat sink ridges unlike the iron caliper.