We offer both type 18-8 & type 316 stainless steel nylon insert lock nuts. For salt water or chlorine pools type 316 is required. Type 316 stainless offers superior resistance to corrosion. 
Seize/Galling Warning: Using power/air operated tools to apply nylon insert lock nuts to screws or bolts will produce heat. This heat can cause the nylon to soften and seize. Anti-seize is a good idea when using these type of lock nuts.

Do not combine type 18-8/304 stainless bolts with 316 stainless lock nuts! This has been known to result in galling or seizing up.