This is a standard 14mm switch boot made of injection molded silicone rubber. The inside of the boot contains a "nub" that can be trimmed to length to suit your application.
Trimming the nub completely flush will allow this boot to fit like the standard McClicky boot, but this material has a softer feel.
Please note: My supply of GITD and Prometheus Blue boots is unreliable. I like to have these on hand for customer lights and since I never know if I can order more, these are more expensive.
The switch retaining ring must be SNUG (not gorilla tight) to ensure reliable contact. If you swap out the boot and the switch behaves erratically, the retaining ring is probably installed too loose. If the button seems "too sensitive" the retaining ring is too tight.