The utility model provides a curved shell fragment that electric special fastener device is got to terminal row, the surface of insulator is the cambered surface, and insulator sets up the penetrating groove of passing through along length direction, the one end of insulator one end periphery erection joint piece, the other end installation extension head of connecting block, the insulator touches with the extension head mutually, and the insulator passes through connecting block and the first fixed connection of extension, and prolong first outer wall and be equipped with several opening orientation along the border direction and prolong the head. In the carrier roller device, passing through the inslot and touching mutually at the insulator is inserted with the extension head to the plug, the extension head is pegged graft with the terminal row slot and is cooperated, the shell fragment sets up in the extension overheadly, the elasticity of shell fragment makes between extension head and the terminal row slot fixedly more firm, prevent that the extension head from droing from the terminal row slot, the connecting block cooperatees with terminal row slot mouth, inserting, it is more convenient when first to pull out the extension, this kind of structure can prolong plug and the terminal row slot distance between, make things convenient for the staff to operate the plug of carrying out the plug.