The 507 mm (24" decimal) size fits juvenile mountain bikes and cruisers.
This does not fit fractional sized tires such as 24 x 1 1/8, only tires marked in a decimal width, such as 24 x 1.75.
The 1.5- 1.9 fits the 24 x 1.4 to 1.9 tire size.
The 1.9-2.0 width tube is the standard size for tires marked 24" x 1.9", 2.0", or 2.125".
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.
|24x1.5/1.75 Schrader Valve||TU5732||TUL24|
|24x1.9/2.0 Schrader Valve||TU5734||TUL25|