The 1990-1996 Nissan 300zx OEM Turbo to Downpipe Stud screws into the turbo exhaust housing and holds the downpipe in place. The Z32 turbos have two of these studs in each turbo and these studs are made from Inconel to hold up to the extreme heat.
When upgrading to aftermarket turbos they often do not include these studs and we recommend getting them when you purchase the new turbos. For 4 Bolt turbos like the Sport 500, Sport 600, and Gt525 you will need 2 studs per turbo. For the 5 Bolt turbos like the Sport 530bb, Sport 550bb, Sport 700bb, GT600r, EXP90, etc you will need 3 studs per turbo.