This 3.00-4 inner tubes (innertube) is commonly (though not exclusively) associated with 37cc to 49cc pocket bikes, mini bikes, mini choppers and other miniature powersports products. Most commonly used for 47cc to 49cc air cooled and liquid cooled pocket bikes, mini racers and mini bikes.
 
Commonly associated denotations:
2.80-4
3.00-4
8x3.00-4
260x85