Socket Shoulder bolts are fasteners that have an unthreaded portion of the shank that functions as a bearing surface or spacer.
These are measured by the Shoulder Only, for this size the shoulder diameter is 1/2", the length of the shoulder is 2 1/2" and the thread on the end is 3/8 16 TPI UNC.
It is important to note the threaded portion is NOT included in the length.
They have an in-hex drive and are fastened using a hexagonal wrench also known as an Allen key. Use Allen key size = 1/4"