To perform miniaturization, to reduce weight and to easily perform carrying by engraving a helical groove on the outer peripheral part of a main body formed in an U shape by folding back a flat cylindrical body from a central part.

The helical groove 4 is engraved on the outer peripheral part of the main body 1 formed in the U shape by folding back the flat cylindrical body provided with opening parts on both ends and provided with curved surface parts 2 on both side faces from the center part. At the center of both end edge parts of the main body 1, a handle to which a safety link 9 is externally fitted is fixed by a fixing fitting 8 and the helical groove 4 is successively broken and linearly expanded when loads are applied to the main body 1.