CTS (copper tube size) x CTS X CTS compression tee for Type K or L copper tube, ASTM (American Society for Testing and Materials) D2737 SDP-9 Polyethylene tubing, ASTM F876 DSR-9 PEX tubing, and ASTM D2666 SDR-9 Polybutylene tubing. Brass fitting includes EPDM (Ethylene Propylene Diene Monomer) Rubber gasket, anti-friction ring, Mac-Pak nut with split clamp, and stainless steel screw. Insert stiffener is required when used with plastic tubing.