This is an umbrella pole insert for the Sofun 60 lb. Plastic Patio Umbrella Stand. The stand itself can be used as either a planter or a table, and this insert is for the table top.

The problem I faced is the hole is too large. Not only does it look unfinished, it allows the pole to move. This takes care of both problems.

I measured as follows:
inner - 38mm (umbrella pole)
outer - 50mm (table top)

This print provides for 1mm of clearance and can be snapped into two pieces for easier insertion / removal.