The spring will release when the torque *at the wrench head* reaches the value you have set (assuming the wrench is calibrated). This will be will be consistent regardless of the extension you have attached as long as the setting does not change. The torque at the wrench head will equal the force you've applied times the distance from the point of application of that force to the wrench head.It's going to release at the setting it's set to...........which is based on one pound at one foot, for ft/lb settings.
The torque at the end of the extension, however, doesn't simply scale as a function of torque and distance, it's a function of *force* and distance, the force being the force you've applied and the distance being the distance from the point of application of the force to the end of the extension. It does not matter that the torque in/on the system somewhere in between (say, at the wrench head) is less, the torque at the extension end is a function of total distance (wrench plus extension) times force applied.
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