New old stock plastic toolbox tube for any bike you can make it fit on.
You can sometimes find these on Italian mopeds. They are made to bolt through the seat post clamp and sit under the seat. We love slapping these on any bike though. They are perfect for a little bottle of oil, a spare plug, and a compact plug tool. Put whatever you want in there though!
Mount is 27mm wide.
Tube interior is 125mm deep and 54mm in diameter.
Made by Metalplast.