When available, trees are used to support field telephone wires. Wire is strung through the tree branches. When the wind blows, the branches move, creating chaffing on the wire insulation. When waxed cloth insulation is used, this chaffing can strip the wire bare. With some circuits, a short to ground via the tree can be created. With double wire (La + Lb) circuits, a short circuit can be created between the two wires.
To get around this chaffing problem, tree hooks (Baumhaken) or porcelain insulators (Isolierporzellanrollen) are used to support the wire in trees.
Tree hooks can be entirely made of steel wire or made of cast metal and steel wire. At the top of the wire hook is an eyelet (Öse). Near the bottom of the hook is tight coil of wire (Tülle) which is used by the wire fork (Drahtgabel) to place the hook on a tree branch. Wire is passed through another coil of wire (Kabelführung) at the bottom of the hook. The Kabelführung is electrically insulated from the hook by a rubber insulator (Isolierrolle).
The cast metal steel wire version of the hook basically has all of the same parts.
Porcelain insulators are basically the same used on farms for electric fencing. They are screwed into the trees using wood screws. Wire is held in place with metal spring clips.
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WW2 German Field Telephone Equipment 