1/2 inch Essex Flange - adds a 1/2 inch female BSP threaded connection to a hot water cylinder / tank.
The popular Essex flange is the easiest and fastest method of making very sound tank and boiler connections for all sizes of pipe work and immersion heaters. There is no need to get at the job through the top cap in a tank or cylinder because connections using Essex flanges can be made in awkward places by cutting a hole and fitting from one side only without the need to remove the vessel.
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.