Another turbo question

I'm embarrassed to admit this but can someone help me understand which one is the right one. I have a S-13 SR20det red top I want to upgrade the turbo to a Garrett t28 ball bearing for fast spooling and overall performance . I have seen some that say S15 others that are T25 housing and even a T3 what is the difference thanks.

Use the S15 T25 style housing because it bolts directly onto your SR20DET manifold. 'Nuff said.