Leica no longer sell their original plastic part to independent repair shops, requiring you to send your lens to Germany to replace the part at an exorbitant cost for a trivially easy job. Anyway, the original part is rubbish - doesn't provide a good grip and breaks easily. My designs provide a more secure grip, and won't break like the plastic version. They are also designed so that in the unlikely event that you fit the tab with enough force, it comes off before the lens itself is damaged. They affix without gluing the tab to the lens, and are perfectly removable if you want to swap it out for a different one or back to the original spec.
All of my focus tabs affix to the lens with an M1.6 nut (not supplied) glued into the back of the focus tab. An M1.6x3mm screw then screws into the tab from inside the lens (the head of the screw may need to be filed down to fit).
See these threads here for details; RFF
All focus tabs are available in Brass (US$35), Matt Black Steel (US$35), or Silver (US$65).
Enquiries for tabs for other lenses welcomed.