There are cheaper options available than those shown by Jazzcnc. I bought a box of ten for about £12 when I built my router some 5 years ago.

One was clearly the wrong type - the fact that it had only two wires, not three, was a clue. One was faulty from day 1 - as I discovered after wiring it in. Since then, two have failed in service. I think that means that I have now finished the box, so if any more fail, I'll be looking to buy from a reliable source!