Conclusion  In conclusion, bolts that were tightened via nut (test cases 2-1 and 3-2) produced similar nut factor ranges  (K = 0.11 to 0.18) as those typically found in literature for “lubricated” steel bolts (K = 0.12 to 0.20)  regardless if lubrication was added to the faying surface under the nut or not. In all published sources  reviewed, if the term “lubricated was defined it meant lubricated at the threads and “non-lubricated” would  mean no lubrication was added to “as-received condition, but bolts were not specially cleaned to remove  any residuals from machining/processing. Of course, if lubrication is added to the threads it can very easily  migrate to the nut faying surfaces hence explaining the similarity. However, for bolts tightened at the head,  there are some significant differences. If lubrication exists on the faying surface of the bolt head (test case  1-2, 2-3 and 4-1), nut factor ranges typical for nut-tightening were produced (K = 0.1 0 to 0.21), but if there  was no lubrication on the faying surface of the bolt head (test cases 1-1, 2-2, 3-1 and 4-2), the nut factor  ranges were significantly larger (K = 0.18 - 0.56). It made little difference for the bolts tightened via head  whether it was threaded into a nut or insert.  A fairly comprehensive literature search was performed to look for nut factor data on bolts tightened at the  head or effects of additional faying surface lubrication. Nothing specific was found. However, one source  had a very brief statement that acknowledged K values could be “up to 50% higher” for bolt head  tightening 111. It is very clear from this testing that general “text-book nut factors values can not be  assumed to be appropriate for non-lubricated faying surface bolts tightened at the bolt head.  Testing demonstrates that as early as the second cycle the nut factor increases significantly when  tightened at the head without lubrication at the faying surface. This change in nut factor needs to be  considered for reworking of a nonlubricated bolted joint or where a mix of installation cycles exists in a  critical joint to maintain the desired preload.  Torque tension joint specific testing was not required for the majority of ISS Space Station hardware. Test  results indicate that for future programs, testing should be considered for critical joints where it is not  possible to apply lubrication at the faying surface.  References  1. Engineering Sciences Data Unit “Applying, Measuring and Maintaining Pretension in Steel Bo!ts.”  2. National Aeronautics and Space Administrations. “Standard, Threaded Fasteners, Torque Limits for”  3. Gibson, James N. “Torque Tension Tests for the Common Berthing Mechanism (CBM), International  4. Morrison, Raymond F. Analysis of CBM Bolts for Overtorque Condition” Boeing Report D684-12216-  5. Shigley, Joseph E., and Mischke, Charles R.(1996). Standard Handbook of Machine Design. 2”d ed.  6. Bickford, John H. (1 995). An lntroducfion to the Design and Behavior of BoltedJoints. 3rd Rev ed. New ESDU Item Number 8601 4, July 1986  MSFC-STD-486 Rev B, November 1992.  Space Station” Boeing Report M&P-3-1638, June, 2005  01, June 2005  New York: McGraw-Hill.  York: Marcel Dekker.  1 62