9-Plus also offers a Heavy Duty Housing patterned after the later-style Ford 9-inch unit. However, the 9-Plus has been specifically formed to accept 3-inch O.D. tubes that will slide right in. The original Ford housings required a 3-1/4" diameter tube which is not compatible with many of the commercially available brackets commonly welded to the axle tubes. The 9-Plus Heavy Duty Housing is designed to permit the axle tubes to go into each side up to four inches. Slots are machined in the housing ends to provide additional welding contact. This housing is made of premium forming steel for wrinkle-free forming. This 9-Plus Housing is made of a slightly thicker gauge of steel than a stock 9-inch housing for more strength and stiffness, and a better base for welding brackets to the housing without distortion. This housing is commonly used in high powered street machines and professional racing applications.