12-20mm fits 1/2" hose, 16-27mm fits 5/8"-3/4" Hose. High quality stainless steel hose clamp also known as smooth band clamps, these have a non-perforated band with rolled edges to prevent damage to hose and tube. Band is 3/8" wide and 0.024" thick. Tighten screw with a slotted screwdriver, Phillips screwdriver, or 9/32" (7 mm) hex nut-driver.
Recomendations:
(12-20mm) Fits 1/2" Hose
(16-27mm) Fits 5/8 - 3/4" Hose