1/2" and 3/8" Plastic barrel cap socket wrench adapters for 208 l (55 gallon) barrels.

There are 4 models in total, two for the small cap and two for the large cap for ½" and 3/8"  socket wrenches.

Works well with my custom caps: https://www.printables.com/model/919456-plastic-barrel-bung-caps-with-gardena-hose-connect 
as well as with the original caps.

Print with a high infill for strength. PETG prefered.