Are you stuggling for traction, or just have some terrible noise coming from the GM 12-bolt in your truck? Hurst Engineering Limited Slip Differentials offer great traction and strength, but are not overly aggressive for the street. These differentials are 4-spring, composite, clutch-style, limited-slip carriers-with internal gears machined from forged 4320 steel and stronger teeth. These differentials are for GM 12-bolt 30 spline rear ends, and are compatible with 3.73-UP ring & pinion gears. Get rid of that old open differential and upgrade to a limited slip unit!