[Jim Sims]

I not saying the torque method is of no value, I'm saying the stretch or extension measurement method is superior. A nominal fastener situation in which the tension achieved is only measured by the torque applied has to be designed to work within a broader range of actual tension which in practice means the lowest likely value of tension and hence a lower joint performance. If the friction is higher than assumed the fastener will be under tensioned; if the friction is lower than assumed the fastener may fail from excessive combined torsional and axial stress during tightening. The way ARP solves this dilemma (and there are other strategies) is to more tightly control friction. ARP supplies both extension (stretch) and torque values for their fastener hardware. The torque values provided are very specific to ARP hardware (down to the actual part number), using their specified lubricant and five tightening cycles to smooth down the asperities on the friction surfaces - these torque values were likely confirmed (calibrated) by stretch measurements or load cells in the fastener grip. Visit the ARP website for more information and read what they say regarding the merits of the two tensioning methods.