So far I've only put O-rings on my SA spacebars. To reach 7mm I used 3x2mm + 1mm. It helps, but I would like to try SA on the new MX pink switches some day. I mean, if you put O-rings on every keycap, that's a helluva lot of rubber to have to replace when they dry out and rot. I'd rather not have to install them in the first place, y'know?