Whatever did we do before the invention of the zipper？ In 1893 the world’s first zipper was produced in Chicago． Although the inventor claimed that it was a reliable fastening for clothing，this was not the case．The Chicago zipper sprang 51．______ open without warning，or jammed shut，and it swiftly lost popularity．Twenty years ago a Swedish-born engineer called 52．______ Sundback solved the problem．He attached tiny cups to the backs of the interlocked teeth，and this meant that the teeth 53．______ could be enmeshed more firmly and reliably． At first zippers were made of metal．They were heavy，and if they got stuck it was difficult to free．Then came nylon 54．______ zippers which were lighter and easier to use，and had smaller teeth．The fashion industry liked the new zippers far better because they didn’t distort the line of the garment or weighing 55．______ down light fabrics．They were also easier for the machinists to fit into the garment． Meanwhile a new fastening agent made its appearance at the end of the twenty century: velcro. Velcro is another product 56．______ made from nylon．Nylon is a very tough synthetic fibre first developed in the 1930s，and bearing a name to mind the wearer 57．______ of the two places where it was developed：NY for New York and LON for London．Velcro is made with very small nylon hooks on one side of the fastening which caught tiny looped whiskers on the 58．______ other side of the fastening．It is strong and durable． Velcro is used on clothing，luggages and footwear．It is quick 59．______ and easy to fasten and unfasten，and has taken a large part of the zipper’s share of the market．It is also used in ways a zipper cannot be used—for instance as an easily changed fastening on plaster casts，and to hold furnishing fabrics in a position． 60．______