These fittings are great for adding a temperature or pressure gauge to an engine that does not have a tapping in it.
You order the correct size of fitting for the flexible rubber pipe on your engine. The size quoted on the fitting is the flange size not the flat behind the flange. So if you need a really 'snug' fit order 2 mm smaller than the internal dimension of your pipe.
Cut into the flexi hose.
Pass the supplied screw clips over the flexi pipe.
Push the fitting into the open ends of the flexi pipe. A smear of washing up liquid will help it slip in.
Pinch up the screw clips. Be careful not to go too tight to begin with, you can always tighten up if you need to.
Screw in the temperature sender, you will want put some PTFE tape on the treads first. Sensors come in all fitting sizes. You will find that if you need to change the size there is plenty of meat on this fitting so you can drill and tap it to match your fitting.
The last job that you need to do is run a negative wire back to the battery.
Then you should be good to go.