This mechanical flange adapts a copper cylinder to accept an immersion heater element.
Standard immersion heater 2-1/4 inch BSP female thread.
The male part of the fitting that goes through the cylinder has a 2-1/4 inch BSP thread, this measures about 65.7mm diameter, so the hole in your cylinder will need to be a little bit bigger than that.
** BSP thread sizes are measured a special way - have a look at our information page for more details **