From left to right.
1. Coupling- female to female thread whatever size the thread is for the heating element.
2. Bushing- male to female used to reduce to a smaller thread.
3. Strain Relief- This is prevents the wires from being yanked out of the heating element if the cord is pulled. It is common in industrial electrics. part of it is just like a buld head and then the wire slides through. The cap on the right hand side screws down (usually with some type of seal) tight on the cord. Some are available liquid tight.