Harbison published two versions of his Trio Sonata. One for OB/EH/BSN and the other for 2CL/BCL. If you want the Trio Sonata for OB/EH/BSN order 50482451. If you want it for OB/CL/BSN (Harbison notes that the sets are interchangeable for any trio combination), then you need to order both versions. If this is confusing, please call or email TrevCo for further clarification.