Coarse Kosher Salt In Salt Mill We recently are starting to run out of coarse sea salt, and I was wondering if it is okay to substitute out coarse sea salt and instead use coarse kosher salt to grind inside of a stainless steel grinder salt mill. Are there any real differences and which would you recommend personally? I would really appreciate the help!
There's no chemical difference between the two, assuming they are both sea-salt originally. Kosher salt tends to be more in flakes composed of small crystals than coarse sea-salt, which is a more rough individual crystalline form. 

Both should work just fine in your grinder, though the spacing between the two surfaces of the grinder might affect how well each type grinds in the mill.