We change the light on our lamp post and no longer wanted a crossbar, this simple plug fills the hole left over. The hole to fill was .75 inch and this print fills that hole with a little flange around it.  Version 2 would be to get the curvature of the post to match but didn't want to spend that much time.  This was printed in PLA but since it is for the outdoors it should probably be printed in PETG