"Rick & Linda Bernard" wrote in
:

For a Marine designation there are probably some upgrades. Stainless
contacts and probably a sealed circuit board. Perhaps some spray
proofing. Maybe powder coated vs paint and maybe more non-sparking.

Add this to a small market and you get the $40 markup. Perhaps
someone could write Vector and ask what is the difference in the plain
vs the -M model.

Look at both. No difference...nada.