18650 means 18mm x 65mm. Of course, they're rarely that precise. I measured a few I have and they range from just under 18mm up to a hair over 19mm. Since they only come in 14mm or 18mm, the 18mm would be your only option but you should measure your battery first. A set of chassis discs contains full, half and quarter discs so you still have options even if the full discs do not work.