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 M20 nuts and bolts that take a 30mm socket.
These fit some racks made outside of the USA, such as BLK BOX and Cluster Fitness.
Sold as a pair.