8.8" differential Fits 31 spline axles Torsen T-2 type differential Features full time torque-sensing, torque-biasing Fits solid axle and 2000-2004 Cobra IRS with 31 spline M-4204-T28 fits solid axle and 1999 Cobra/Thunderbird/Mark VII with IRS (2000-04 Cobra has 31 spline) PART NUMBER AXLE SPLINE DESCRIPTION M-4204-F318C(2)(3)(6) 8.8" 31 spline Traction-Lok M-4204-A28(2)(3)(5) 8.8" 28 spline Auburn HD M-4204-T28(4) 8.8" 28 spline T2 Torsen Differential M-4204-F31A(3) 9" 31 spline Traction-Lok M-4204-F28A(3) 9" 28 spline Traction-Lok NOTES:(1)Off-road use only!(2)Will accept anti-lock exciter ring.(3)Requires 4-ounces of CM-19546-A1 friction modifier with initial fill.(4)M-4204-T28 fits solid axle and 1999 Cobra/Thunderbird/Mark VIII with IRS (2001-04 Cobra has 31 spline).(5)Recommended for street use only.(6)Fits 2003-04 Cobra.