It is the rubber strap of a bicycle torch which wraps around the handlebar. The problem I face is it is a triangular shape which decreases in size towards the end. Here is a sketch of it: https://lh6.googleusercontent.com/MRld7xIW70iCcBN4n4V96RA6ssl5qSNGqz1iB5Fs9AM=w276-h207-p-no