One soIlid end cap with center divot. This end cap fits all our premium tubes.
It is 18mm thick, OD = 43mm, ID = 38mm. It's great to have an extra one on hand especially when installing a drain.
These end caps are thick enough to drill your own pin holes so you can use your pin wrench to open and close the tube (see photo) or install a drain.
Most folks like to have a couple extras in their tool bag.