Provided they are run well below their rated Max voltage and current ratings they tend to be ok. ie: if Max voltage 36V run them on 24V or if 50V run on 36V-40V.

It's not exactly big bucks to try them is best way to look at it, but like most things in life you do get what you pay for.!. If these are for your Lathe then they will more than likely be fine because they are not working very hard.