This is a sleeve that protects the notoriously fragile lip on RJ45 (Ethernet) plugs. This was modelled after similar sleeves on factory-made cables. The design is simple but I have found it to be one of the more effective solutions.

This must be printed in a flexible filament, such that the two tabs can move sideways when pushing down the connector lip. A flexible filament will also allow the sleeve to bend and make it much tougher. I recommend a rather hard flexible filament. A softer one could make it easier to fit the sleeve onto cables, but the tabs that protect the lip might become too floppy to offer the required protection. I used the ‘flexible PLA’ from rigid.ink which is very good for this application.

If you do want to print this in a non-flexible filament, you must use jonnieZG's remix instead. Otherwise you will be unable to push the sleeves into the plugs because my models are made under the assumption that the filament is flexible. The ‘teeth’ that must be pushed into the plug end are slightly too wide such that they provide a nice press fit. The remix has more exact tolerances for this part, making them usable with filaments that don't bend.

This is intended to be used on cables that you crimp yourself and obviously it must be put in place before you crimp the plug onto the cable. In theory you could also fit the sleeve on a cable on which you've already crimped plugs, if you slice open one side of the sleeve such that it can be pushed onto the cable, or even just cut the whole sleeve in two halves and then glue them back together.
If you would want to fit this onto a cable with a factory-moulded sleeve, you could cut away the existing sleeve but it may be less effort to just cut off the existing plug and crimp a new one…

For a really solid mount, you may want to add some glue in between the sleeve and the plug.