Flip the Watch Over: Look closely at the round sensor array on the backside of your watch. The model name and size (e.g., Galaxy Watch 6 44mm or Venu 3S) are usually engraved or printed in a circular pattern around the glass sensor.Measure the Lug Width: Use a ruler to measure the gap between the two metal horns (lugs) where the strap attaches to the watch head. If the distance is exactly 20 millimeters, this strap will fit your device perfectly.