PROBLEM TO BE SOLVED: To provide a nesting prevention tool for a armband that surely closes an opening of an end part of the armband. A nesting prevention tool (10) can close an opening at an end of a arm (A) having a pin insulator (Pi) attached to the end. The nesting prevention tool 10 includes a bottomed box-shaped cap body 11, a grip portion 12, and a collar portion 13. The cap body 11 can open one end and cover the end of the arm A from the outside. The grip portion 12 extends in the outer peripheral direction of the cap body 11 and can be gripped by the pair of grip arms 5 a and 5 b provided on the tool portion 52 of the insulating operation rod 5. The flange portion 13 extends from the opening side of the cap body 11 and has a cutout portion 13d cut out from the tip edge. From the state where the support bolt Bs is introduced into the cutout portion 13d, by fastening the nut member N screwed to the support bolt Bs to the collar portion 13, the nesting prevention tool 10 can be fixed to the end of the arm A. [Selection diagram] Fig. 1【課題】腕金の端部の開口を確実に塞ぐ腕金用営巣防止具を提供する。【解決手段】営巣防止具１０は、ピン碍子Ｐｉを端部に取り付けた腕金Ａの端部の開口を塞ぐことができる。営巣防止具１０は、有底箱形のキャップ本体１１、把持部１２、及び、鍔部１３を備える。キャップ本体１１は、一端部を開口し、腕金Ａの端部を外側から覆うことができる。把持部１２は、キャップ本体１１の外周方向に延び、絶縁操作棒５の工具部５２に設けた一対の把持腕５ａ・５ｂで把持できる。鍔部１３は、キャップ本体１１の開口側から延在し、先端縁から切り欠いた切り欠き部１３ｄを有する。切り欠き部１３ｄに支持ボルトＢｓを導入した状態から、支持ボルトＢｓに螺合したナット部材Ｎを鍔部１３に締結することで、営巣防止具１０を腕金Ａの端部に固定できる。【選択図】図１
