There two methods to tighten your Social Battery pin slider:
1) Soldering with a home soldering kit.
This method is the best if you want a strong and permanent result. Solder the washer to the back of the pin using a metal wire. Any soldering kit and metal wire in your toolbox will do! Or you can grab a set here.
See how to do it below:
2) Superglue/Putty. This is a quick and easy method if you are not keen to solder. Use a tiny dab of superglue or putty to fill up the gap between the washer and back of the slider. Adjust the amount according to how tight you want the slider to be.
Tada! Hope this helps!