Intended for compressed air lines only. 300 PSI maximum rated working pressure. Includes one each: No.12-225 1/4" Male NPT Plug and No.13-235 1/4" Female NPT Coupler. Design is considered the industrial standard. Identified by the 3/16" pilot and flat bottom V-shaped ball groove. Due to their large size, do not connect or disconnect if the line pressure exceeds 40 PSI.