Some surface grinder wheels are held on the arbor with a LH nut.
In addition to Chryslers mentioned above, International had some LH wheel studs also.
So, is this info in a manual somewhere, or is it things you just have to learn as you go?
I've done some research on the thermocouple that I replaced, and there it is - right in the service literature. Never in 30+ years of service work on furnaces and water heaters have I run across reverse threads on a thermocouple fitting. Very specific routing of the thermocouple lead, a particular clip in a certain spot, and no bending for installation except near the nut end. Weirdest thing I've ever seen. 2004 WH - first time I've had to replace the T-couple.
I haven't been able to find out why they used such a weird thermocouple. I'm hoping the universal one I installed is acceptable - I'm checking constantly for overheating and other signs of malfunction. I hope them putting a reverse thread fitting on it was just to prevent the use of a non-OEM thermocouple.