Harbor Freight Hercules circular saw fence
The Harbor Freight Hercules circular saw comes missing one thing, a saw fence or guide. It has the slot for it and comes with the screw to tighten it in place, but it's missing even as an accessory purchase.
The guide is easily 3d printed. It has a spot for a 6mm bolt to thread into and a slot for the guide rail to attach. The guide will require support for the slot.
The saw has a 12mm x 4.25mm guide rail size. I used a piece of 1/2" x 1/8" bar stock I got at the local home center, length is your choice but 12 to 18" long should cover most needs. Since 1/2" is 12.8mm, I carefully ran the edges across a belt sander and then a file to finish it down to 12mm wide where it slid in and out of the saw nicely. You should also file the burrs off of the corners.