What goes up must eventually come down. To fight the inevitable effects of gravity on your lines, take advantage of the lightweight Aluminum Clothesline Tightener. Use with fixed line or pulley systems and never mess with burdensome knots again! Thread your line through the spring-loaded center and pull the clothesline to tighten. 3 ball bearings grip your line keeping it taut and the spring action center prevents it from slipping. Say no to sag.