An extension spring body may be adequately stressed while the hook fails early from local bending, side loading or tool marks. The end should be treated as a critical load path.
Start with assembly
Machine hooks, crossover loops, side hooks, extended hooks and threaded inserts solve different assembly problems. Define the installation motion, pin diameter, envelope and retention need first.
Control stress concentration
The hook root contains a strong geometry transition. Tight radii, sharp changes and off-axis loading increase local stress, so cyclic loads should follow the spring axis where practical.
Make initial tension measurable
Initial tension controls the force before coil separation and affects assembly feel. Specify a measurement method, test length and tolerance instead of relying only on visually closed coils.
RFQ inputs
Provide hook orientation, opening direction, critical dimensions, maximum extension, target loads and life. Include mating-pin dimensions and a motion sketch when the hook runs on a pin.
References
This article is informed by public standards catalogues and industry engineering resources. Project values should be confirmed by drawings, material certificates and sample validation.