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