A cap that goes on top of a T-post to help support grapevines and the trellis.  I ended up having to place T-posts to support grapevines as they were overloading my wooden trellis. The cap mitigates the T-post abrading the grapevine. It fits regular(1.25lb/ft) and heavy duty(1.33lbs/per) US T-posts. I made it to flex around the T-post studs and to have enough clearance that if the top is really malformed(within reason) from pounding in the T-post it should still work. I printed mine out of PETG. I would recommend the same for anybody else for the UV and temperature resistance for being outside.