Current batch of box labels is incorrect. These product details are correct.

Thread Diameter: 5/16″-18
Shoulder Diameter: 3/8″
Shoulder Length: 1-1/4″
Overall Length: 2″
Material: Steel
Finish: Plain
Head Style: Socket (3/16″ Socket)
Thread Size: 18 (Coarse)
Thread Length: 1/2′
Hardness: Alloy Steel
Style: Socket Head
Type: Shoulder Bolt

Box of 3.

A shoulder screw differs from machine screws in that the shank is ground to a precise diameter, known as the shoulder, and the threaded portion is smaller in diameter than the shoulder. Shoulder bolt specifications call out the shoulder diameter, shoulder length, and threaded diameter; the threaded length is fixed, based on the threaded diameter, and usually quite short. It is usually used for revolving joints in mechanisms and linkages; when used as a guide for the stripper plate in a die set its called a stripper bolt.