BTW, what IS the most important bolt? The one holding the nut at the throttle??
I remember when the bolt holding the drawbar assembly fell out on 4449's trip to the Whirled Fair in '84. It had been pushed up from the bottom and the nut put on top instead of putting the bolt in from the top, as the latter operation involved some tight clearances. If it had been done right, it wouldn't have fallen out even after the nut worked loose.
THAT was the most important bolt. According to a small book I found in a book shop: The Traveling Engineers' Examination Book, Revised July, 1930: P. 65 Q. 348: "What is most important bolt or nut on locomotive?
A. The loose one. It should be cared for immediately."