I too bought a box of 10 from China.

The machine I have from MD had end-on axial sensing and I crushed a sensor whilst jogging (the machine, not me!), In my naivety I ordered a replacement from MD and it cost £17.50 (ouch, ouch,ouch). When I crushed that one, I ordered 10 from China and converted the sensing to bypass.Some have orange sensor ends and a grey cable and some have blue ends and a black cable. I have 9 of them left. They are all NO and 4mm.

Cheers,

Rob-T