Standard type 18-8 stainless steel hex nuts. Size is 1/2-20 which is considered a fine thread (20 threads per inch) These are for bolts that have a 1/2" thread diameter and are fine thread. The hex on this nut measures 3/4" (flat to flat) and they are 7/16" thick. You will receive one pack of 25 nuts total. 18-8 stainless steel in non-corrosive but is not designed for salt water or chlorinated water applications.