The 

 is a steering universal joint or coupler used in automotive steering systems, primarily for connecting a 1-inch double-D (DD) shaft to a 3/4-inch 48-spline shaft. It is available in different materials, most commonly steel and stainless steel. Steering Universal Joint,

Steel, 1DD X 3/4-48, 3-1/4″ Overall Length, 1-5/8″ Outside Diameter.