Need assistance! I am in the process of replacing a shower cartridge but this project has been halted at it's first step removing the handle to obtain access to the cartridge. I have tried various things all of which has had the unfortunate event of stripping the screw set head so that there isn't anything to grip when I use the allen key to unscrew it. Does anyone know how I can remove this screw set which locks in the handle. The shower handle etc. is made by Delta. Thanks Alex.

I don't see where you have much choice. You have to drill out the Allen Set Screw.
You may then use a self tapping screw to replace the old handle or simply purchase a replacement from Delta. Good luck, tom

Thanks again, things worked out perfectly