The Big Bolt is a imperial bolt.
 7/16 diameter
14 thread pitch
The Smaller bolt is in imperial bolt.
1/4 diameter
20 thread pitch
The sheet shown is how we determine what drill bit size to use for the initial hole.
Drilling in the Bigger sized hole to be taped and died
Drilling in the Smaller sized hole to later be taped and died
In the gif shown on the left I am dyeing to create the threads for the bolt
torque identification chart
Images of my notebook when making my calculations.