I bought some string lights from Amazon: https://a.co/d/iRltSXr

The lights worked fine, but I ended up needing to cap a couple of the sockets. For most string lights, they use an E26 base for the socket, but not the ones I bought. They have the opening for an E26 bulb, but the actual socket is an E17 thread. These are designed to cover the opening of an E26 bulb, but are threaded at E17. The "regular" version is 31.8mm long and fit my string lights perfectly. If you need a other sizes, I included a tall (34.6mm) and short (27.6mm) version of the socket covers.

This is remixed of 2 different socket covers and the original designers are listed in the remix section. I added a slot for a flathead screwdriver for easy install and removal.

I printed mine with Anycubic PLA+ filament. My string lights are LED and use very little power, but be careful using any socket covers. I take no responsibility if something was to happen using these covers. Use them at your own risk.