This is a compact and low cost wrench that's useful for removing and installing pieces that you reconfigure often, or for just helping you hold opposing parts during assembly.
You can use these over the top of your bolts and nuts as wrenches, or you can permanently install them by running them in reverse and using a spot of glue.
These fit 5/8" nuts and bolts that take a 15/16" socket. This size is commonly used on the Rogue Monster Lite series and the Titan Fitness T-3 and X-3 racks.
Sold as a pair.