I assume you have eVolve, since you're posting this in the eVolve Mechanical Users forum, so the parameter you are looking for is "eM_Length A".
If you're looking for both rods on a trapeze, its "eM_Length A" and "eM_Length B".
If you don't have evolve, then like David said, you'll need some add-in that maps the parameters from the database or you'll need to use dynamo.