The CMKV Series Plastic Check Valves are 1/8 inch Male NPT by Barb sizes of 1/8 inch, 3/16 inch, 1/4 inch, and 3/8 inch. The flow is from thread to barb. Material / Disc combinations are available in PVDF with FKM, Polypropylene with FKM, Polycarbonate with Neoprene, Polycarbonate with Silicone, Nylon with Silicone, and Nylon with Neoprene.