Differential, 3.90 : 1 for ZR-1 C4 Corvette only.  Ring & Pinion Set 

NOTE: This is a NEW part. No warranty warranty and NO returns after installation.  It is the responsibility of the Customer to insure this differential is installed correctly and is suitable for the use intended by Customer.

Link to Yukon Gear for more details : 

High performance Yukon replacement Ring & Pinion gear set for Dana 44-HD in a 3.90 ratio | YG D44HD-390 | Yukon Gear & Axle