Zipper strategically placed on the bottom for durability & ease of use. Easy to attach to the blower & an adjustable shoulder strap for comfort. Simply fill the bag, unzip the bottom & empty into a container. Bottom zip blower vac replacement bag easy to attach to the blower & an adjustable shoulder strap for comfort simply fill the bag, unzip the bottom & empty into a container fits on models 51539, 51549, 51553, 51573, 51587, 51591, 51598, 51599, 51617, 51618, 51609 & 51619