How to Measure the Diameter of a Stud

Simply put for our purposes, the stud size refers to the width or thickness of the stud or bolt that passes though the eyelet of the battery cable lug.

To find the stud size just measure the diameter of the shank. The shank is the shaft-like part of the bolt or stud. Preferably use calipers to obtain an accurate measure of the shank's diameter, but a ruler works too. In most automotive instances, the shank's diameter is going to be either 1/4, 5/16, or 3/8. 

 Common stud sizes for reference:

• 1/4 - Blue Sea Fuse Boxes (4,6, 8, and 12) / Blue Sea 2300 busbar / Single and Double MRBF Fuse holder / Fender grounding bolt. 
• 5/16 - Switch-Pros Power Stud / Factory Battery Terminals / Bussmann RTMR and RFRM.
• 3/8 - After Market Mil-Spec Battery Terminals