Check valves permit flow in one direction only, and close automatically if flow reverses.
This non-return valve has an internal brass swinging flap and is designed to allow inspection and cleaning without the need to remove it from pipework.
1 inch BSP female threaded connections on each end.
BSP (British Standard Pipe Thread) sizes don’t match up with what you would measure using a ruler. Have a look at the BSPT link at the bottom of this page for more information about how plumbing threads are measured.