Bolt with built-in tensile strain gauge - photo and patent

[Jon]

Don't want to get lost in semantics here, but I should point out technically that I believe these bolts measure preload as opposed to torque. And I guess the advantage here (and the justification for $20 bolts) is the ability to roughly measure that preload, and NOT just the torque used to attain the preload? Someone more knowledgeable than me can expand on this.