The topeak fuel tank bag is a large capacity top tube bag with an easy to use velcro mounting system giving you the ideal place to store your mobile phone energy bars wallet or tools while yoursquore out and about this topeak top tube bag is available in two different sizes the large one consists of one main compartment and two inner mesh pockets with the medium version consistion of one main compartment and one mesh pocket topeak fuel tank bag features 1800 den