Actually, these bolts are called Torque to Yield. Yes Chitty, you are correct. The intent of the design is to achieve a constant clamping force such as on the head gaskets. Uneven clamping force can cause premature gasket failure. Since bolts are elastic, if you were to look at stress strain curves, the curve flattens out in the area of yield. so the stress becomes a constant in that area and the clamping force becomes equal for all bolts. They are a one time use only though.