Comparison : Item # 6408-02, 1/8 Inch (in) T1 (NPTF) Carbon Steel O-Ring Hex Head Plug
Item # 6408-03, 3/16 Inch (in) T1 (NPTF) Carbon Steel O-Ring Hex Head Plug
Item # 6408-04, 1/4 Inch (in) T1 (NPTF) Carbon Steel O-Ring Hex Head Plug
Item # 6408-05, 5/16 Inch (in) T1 (NPTF) Carbon Steel O-Ring Hex Head Plug
Item # 6408-06, 3/8 Inch (in) T1 (NPTF) Carbon Steel O-Ring Hex Head Plug