Combination Sucker Rod Couplings Combination Sucker Rod Couplings are used to connect one size Sucker Rod to another size Sucker Rod. Crossover can build these in any of the regular API Grades such as J-55, L-80, or P-110. These are usually only made going up or down one size in either direction such as ¾” to 1” or 1 ½” to 2”. Even though they are not Combination couplings, Crossover can also thread any combination of Sucker Rod Crossovers and Swages.