Top Quality Marine Bolt Supply Stainless Steel 5/16-18 Jam/Thin Nuts These 5/16-18 stainless jam nuts are available in convenient packs of 50. Dimensions are as follows: Width (flat to flat) is 1/2" & thickness is 3/16". 5/16-18 is considered standard coarse thread because there are 18 threads per inch (tpi). Jam nuts are typically half as thick as standard nuts and are useful in tight space applications. Type 18-8 stainless steel is most common. It has a high resistance to rust and corrosion and may be mildly magnetic.