The 305 mm (16" decimal) size fits most 16" children's bikes.
This does not fit fractional sized tires such as 16 x 1 3/8, only tires marked in a decimal width, such as 16 x 1.75 or Schwinn 16 x 1-3/4.
Since tubes are stretchy, they do not need to exactly match the size of the tire.
Depending on stock, size shipped may not be exactly the same as listed in the pull-down menu.
Standard Schrader valves, the same as used on automobiles.