Bookshelf tab for metal & wood shelving units. Similar design to original, but triangular in shape due to stress from weight of shelf. Adjust whichever of the axes you need for your application.
Credit to: Mr. Gluckner

Just ensure size is correct for your application, and I would highly recommend printing it as seen in the “thing” file. The extruded plastic holds up better when the layers are placed vertically. Otherwise, it may split at a layer.