Dabond has it right, especially on thermal expansion. Helped on a study on the B-52 when we were first rigging for cruise missile carriage. Looking at a rotary launcher in the bomb bay, and showed thermal expansion of 6 inches across the width of the bay, with a temperature range of something like -50F to 140F. Steel isn't as bad and I don't have the numbers handy, but if you are going to measure something, be sure the temperature has been stable for a couple of hours. It would be best to take a temp reading on the metal itself, but not many have a surface probe for this. My wife got me a voltmeter that does everything, and came with a temp probe. Gotta love that gal.
