This number is always preceded by a "Ø" symbol. i.e. Ø82 = 82mm lens thread size; Ø58 = 58mm lens thread size.etc. Area of sky most effectively polarized with a Circular Polarizer: Point your index finger at the sun.
K&F CONCEPT 37-95mm Circular Polarizer Filter CPL Filter Ultra-Slim (K Series)
Nisi True Color PRO Nano CPL Circular Polarizer Filter 49 52 58 62 67 77 82 95mm
K&F CONCEPT Ultra-Low Reflectivity Circular Polarizers Filter (Nano-X) 37-95mm
K&F CONCEPT CPL 43-82mm Circular Polarizing Ultra-Slim Camera Lens Filter NANO-K
52mm Phone Lens CPL Polarizer Filter for iPhone,Samsung and Other Smart Phones
HOYA 82MM HD NANO MK II CIRCULAR POLARISER FILTER (82NANOIICPL)