The A-5 mainshaft is formed from 9310 alloy and is recommended for vehicles that produce more than 425 lb-ft of torque at the flywheel. The 9310 mainshaft can support up to 525 lb-ft with the A-5 First-Fourth gear kit and cluster-case support plate, and it also features a 28-spline for the slip yoke, just like the factory mainshaft. The A-5 unit has a way to ensure that the Fifth M/S gear snap ring does not pop off the shaft. All '99-up 3.8L Mustangs have a spot behind the Fifth M/S gear where the electronic speedo drive gear is placed and held in with a snap ring. Astro used this idea to implement another snap-ring groove to ensure that the snap ring did not pop off with its A-5 road race Fifth gear kit.