Marine Grade IMPERIAL/SAE 316 Stainless Steel Nuts

Type 316 stainless offers superior resistance to rust and corrosion and is recommended for chemical, salt water or coastal environments.

Hex: The size of a nut is determined by it's inside diameter (the threaded hole). The hole has to fit the screw/bolt so for example, if you have a size 10-32 x 1" screw you will need a 10-32 nut.

Lock: 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. 

Cap (Acorn): Cap nuts are sometimes referred to as acorn nuts. They have a nicely finished, smooth, rounded head that protects and covers threads. These are often used for cosmetic value. The grade 316 stainless is the recommended for any salt-water or chlorine applications.