Non-current carrying fittings
Fittings of external power lines not subject to special tensile stresses (light-duty connection) shall retain the driver's axle with a clamping force of at least 27% of the mathematical strength of the driver. There must be no slipping of the driver in the armature or rupture of his wires.
Fixed tightening fittings (rigid couplings) must trap a driver's axle with a holding strength of at least 85% of the mathematical strength of the driver without slipping the wire in the fitting or tearing of its wires. This value, which guarantees the strength of the driver's attachment, is referred to in the catalog as the strength of the fastening.