This is a middle connector for creating a frame for the garden from canes.
Internal diameter is ~10mm, and a hole is provided for a screw for canes which are not a snug fit.

see http://www.thingiverse.com/thing:1581046 for a 3 cane (corner) variety.

I printed 4 corners and 2 'middles' in ~7 hours @50mm/s in black PLA using pretty standard Cura settings.