When in Rome!
(Or new facts foil faddist's fallacies)

An article by George Lorimer, Retired;
formly of the G.M. Powertrain Fastener Lab.

George Lorimer

The old adage of "when in Rome, do as the Romans do!" really meant that if you were unsure of the proper conduct of the day or of the moment - copy a native.

Problems arise all over the place with this kind of thinking! For example--

  • One being copied may not be a native!
  • May not be correct!
  • May be drunk!
  • May think you are making fun of him/her and bop you!

The whole lesson here is that when you are going to be in strange territory find out in advance, if possible, what you can expect to occur! The same thing applies to the use of fasteners of the-joint-holding-together-threaded-type (screws, bolts and nuts).

A fairly simple real life joint analysis will clarify a lot about the design of a joint or the choice of a fastener or even the finish on the fastener. An example could be that you want to know what torque would be safe for a given fastener in a joint. The answer would come from tightening several joints to a failure situation and recording the energy needed to drive the fastener and the amount of rotation required to achieve the failure. The rate of energy absorption would tell about the friction in the joint as well as an indication of the type of joint: soft, hard, etc. The total angle traveled could be an indication of the crushability or strength of the joint and/or the total stretch of the bolt. All joints have their own identifying characteristics which are - signatures! These are the traces made during a test to tighten the joint.

If you have a single bolt that is used in several joints - beware the tendency to apply the same torque to all. The make up of the joint will dictate what torque the joint can handle. The bearing surface under the head, whether or not a washer is used, the material of the nut threads. All are determining factors that make up the proper torque specification or tightening strategy. Even the finish of the fastener against various finishes is a large variable. Bottom line is - be aware - not only in Rome but also wherever you are doing the fastening of a joint - critical or not.

A sign in one of my old bosses’ office I saw years ago stays with me – it read:

"One test is worth 1,000 expert opinions!"

Quality is alive and well.

George Lorimer, Retired.
G.M. Powertrain Fastener Lab.