**Edit 2019-04-03 - The length of the tongue that engages the groove in the buffer tube was not long enough and would allow the tube to rotate out of alignment. In this update the tongue was increased in length by 2mm. You will need sand/file it down until it fits nice and snug. I provided the Rhino file for those that want it.
This buffer tube lock ring allows for the use of a sling at both either left or the right side of your AR-15 lower receiver.....Do keep in mind that it is plastic (PLA in the pictures) and will not be anywhere near as durable as it's metal cousins found at various shops, stores and websites where quality gun accessories are available ;).
I am printing an entire AR-15 from butt stock to flash hider and could not find this version of a lock ring....so here one is now.