Fine vs Coarse Thread
All fasteners are available with either coarse or fine threads.
Finely threaded bolts have larger stress areas than coarse bolts of the same diameter, so if you are limited on the bolt size due to dimensional constraints, choose a fine thread for greater strength. When you don’t have much depth to work with, you want to utilise their greater number of threads per inch. Fine threads also have a greater adjustment accuracy by providing more rotations to move linearly.
On the other hand, coarsely threaded bolts are less likely to be cross threaded during assembly. They also allow for quicker assembly and disassembly, so choose these when you will be reassembling apart often. If the threads will be exposed to harsh conditions or chemicals, a coarsely threaded fastener should be considered for its thicker plating or coating.