Product Code:SAE J1305 Title:Two-Block Warning and Limit Systems in Lifting Crane Service Issuing Committee:Cranes And Lifting Devices Committee Scope:The purpose of this SAE Recommended Practice is to establish the minimum performance requirements of devices which signal and/or automatically prevent two-blocking. This SAE Recommended practice applies to cranes in lifting crane service which are equipped with two-block warning and/or limit systems.