Grid indexing: find better names or controls for Ring 1 and Ring 2

Ring 1 and Ring 2 inputs are actually two inputs of the indexing that define a double loop. The indexing has a outer loop that goes through every ring in Ring 1 and another inner loop that goes through every ring in Ring 2, producing every possible matchings (R1, R2).

However, Ring 1 and Ring 2 can be confused with the ring that has the index 1 and the ring that has the index 2.