The fixing of wires to the vertical supports and their non-use period play a major role in the stability of the espalier and the organization of pruning operations.

The solutions proposed during the time were numerous and range from simple two crossed sticks to rotating devices made of different materials, from small pulleys already known in the past to threaded thread-tensioners, not very popular, because they were rendered useless by the early rust. Most popular devices in aluminum alloys, galvanized iron or anodized aluminum, stainless steel and plastic, which allow to rotate only a fraction of a turn remaining fixed to its hooks or with transversal arrests. The thread-tensioner can be placed near the head poles, from one end or both for a very long rows. If mounted centrally the outcome is better, but the non-use period is not practical.

The types available are many: from simple, consisting of Z-shaped iron rods, to tube pieces rotated to wrap the wire and then prevented from turning by a big stud stuck in the transversal holes, to the specific accessories in alloy or stainless steel. They are quite used in France and Germany and now they are being distributed in Italy, the chains in galvanized iron or stainless steel tied at the end of the wire.

The wires shall be periodically stretched because, depending on the material, they are subject to elongation. Fixed thread-tensioners are used for small and medium wires (photo 30), while for large wires (used in single curtain, GDC cultivation systems, etc.) mobile thread-tensioners are used instead.

GRIPPLE THREAD-TENSIONERS

This thread-tensioner consists of a cast aluminum block in which there are two channels, where the wire can easily pass through both of them each in one direction but not in the other, being blocked by a knurled roller when a load is applied. The wires are stretched with the specific pliers.

SUNFLOWER THREAD TENSIONER

Die-cast aluminum thread-tensioner with stainless steel locking in different sizes

SHACKLE thread-tensioners