the present disclosure relates to a locking device for use in releasably securing sliding elements to a line or filament and for cushioning the shock of impact of the sliding element against a line stop . the sliding element has a stop element located in a passage which runs the length thereof . the stop element is then twisted to engage the filament and is prevented from untwising by locking means . cushioning of impact with a line stop is accomplished by the elastomeric bumpers which extend from the stop element out of the sliding element .