For 1994 to 2002 Dodge Ram 2500 and Ram 3500 trucks with Dana full float rear axles (this will include all Cummins Diesel and V10 trucks and all but the lightest duty Ram 2500 models with smaller gas engines), Dodge standardized on a an 4-3/16" wide external snap ring u-joint with 1-3/16" diameter cups. For normal service parts, all you really need to know is if your driveline is a single shaft part with 2 universal joints or 2 shaft assembly with 3 universal joints and a Center Bearing.
The descriptive term "Cardan" refers to a conventional cross type universal joint. A Single-Cardan joint has one universal joint for each yoke. For more information on this subject, see TSB3500 Universal Joint History, Types, General Service Methods, and Inspection; or TM3000 Driveshaft Service Manual.
