Super great POM nuts, just install them upside down, of what the picture shows you here. All Enders 3D printers have mounted the brass nut the wrong way! Go to Youtube and look up anti backlash nuts and see how to mount them.
Very good, much better than stock. Got rid of issues with play in the stock nut that were causing issues with my z height being off. Be aware that although the nut looks like black anodized aluminum is it actually plastic/delrin.