Base reinforcer for 18M fiberglass pole

I imported some 18m long push up fiberglass masts from China to use as antenna masts and wanted to reinforce the base section and center the mast on a ground spike. This print will slide into the bottom of the mast and prevent any damage to the fiberglass section while allowing a ground spike to slip into the centre.

The outer diameter of the part that slips inside the mast is approximately 68mm.