Cup square coach bolts, also known as carriage bolts, are a type of fastener that is used to secure heavy objects together. They have a square head that fits into a matching square hole in the object being secured, and a cylindrical shank that is threaded on one end. The threaded end of the bolt is screwed into a nut, which holds the object in place.
Cup square coach bolts are typically made of steel and are zinc plated to prevent rusting. They are available in a variety of sizes and lengths, depending on the application.