A new physical testing and labeling procedure for shaker screens. To be API RP 13C compliant, a screen must be tested and labeled in accordance with the new recommended practice. Two tests were devised: cut point and conductance. The tests describe a screen without predicting its performance and can be performed anywhere in the world. After identifying the cut point and conductance, complying with API RP 13C requires application of a permanent tag or label to the screen in a position that will be both visible and legible. Both cut point expressed as an API number and conductance shown in kD/mm are required on the screen label. Internationally, API RP 13C is ISO 13501. The new procedure is a revision of the previous API RP 13E, which was based on optical measurements of the screen opening using a microscope and computer analysis mi explicación. Under API RP 13E, screen designations were based on individual manufacturer test methods, producing inconsistent labeling.