Turnbuckle (The direct shear stress induced in screw thread)


A mechanical joint is a part of a machine which is used to connect another mechanical part or mechanism. Mechanical joints may be temporary or permanent. The buckle or a coupler is a mechanical joint used to connect two members which are subjected to tensile loading which require slight adjustment of length or tension under loaded conditions. It consist of central hexagonal nut called coupler and tie rod having right hand and left hand threads. A coupler of hexagonal shape is to facilitate the turning of it with a spanner or sometime a hole is provide in the nut so that tommy bar can be inserted for rotating it. As coupler rotate, the tie rod are either pulled together or pushed apart depending upon the direction of the rotation coupler. Considering a turnbuckle, subjected to an axial tensile force, the direct shear stress induced in screw thread can be calculated by the this axial tensile force, the core diameter of the screw and the length of the coupler nut.

Related formulas


τsThe direct shear stress (N/mm2)
F_τAxial tensile force (N)
dcCore diameter of the screw (mm)
ln Length of the coupler nut (mm)