To Phak1's point and you agreeing. Obviously if you have a bolt that threads into a threaded hole somewhere, you have to use the same threads. The poster himself made this point.
My point was, and to answer the posters question, was that if you find a bolt AND a nut, you DO NOT have to replace it with a fine threaded set. You CAN use UNC without any danger or problem. Also you can use grade 5 anywhere on that truck.
Then the discussion went off on the pro's a con's of fine thread. A true waste of time. Then a discussion of replacing "like with like" without specifying that bolt and nut sets are an exception. That is ridiculous. The question was answered long ago.
I agree with Phak1 also because he agreed with me
.........except as noted.
If you find a fine threaded bolt and nut, do you really know it's factory? The only ones you know are factory are the fine bolts that thread into a factory cage nut or other female permanent thread.
The things you read now on the internet about coarse and fine were not well known or tested or understood in 1946. Fine thread may have just been for adjustment or short engagement. Vibration levels of aircraft, space vehicles, building wind deflection, clamp force requirements, testing methods, alloys, engineering of fasteners and strength of materials were not as well established or known. The use of fine threads in 46 was not for some fear of failure of a coarse thread in a truck on bumpy roads.
