Welcome to ZIPLINEGEAR!
The Eyebolt is a heavy-duty piece of hardware to anchor zip lines to posts. When connecting your zip line to trees, a Cable Sling can be used, but for posts, the Eyebolt works great.
The threads extend part way down the shaft (the length of the threaded portion of the eyebolt may differ from the picture).
5/16"x 3.5" Eyebolt is for light duty use and is not to be used as Zipline anchor.