Nickel EK-ACF 10/13mm Soft Tube Water Cooling: EK-ACF Fitting (Advanced Compression Fitting) is a soft-tube compression fitting, designed for use with flexible soft tubing such as PVC, EPDM, Norprene, silicone or any other type of compatible flexible tube.EK-ACF Fitting is a more secure variant of the tubing fitting connector as the locking ring