They are 510 heat sinks. I use them on all my mods to protect the 510's. I'm constantly switching tanks so the 510 get quite a bit of abuse. Well worth 5 bucks to protect it. These are readily available online. Slow tech has the cheapest price if you don't mind waiting.I have seen some 510 protectors but cant find them now
They are 22mm discs which are about 0.5mm
If I can find them will throw up a link but mentioning them now may bless us with their appearance

Sent from my iPhone using Tapatalk