Re: Socket Head Screws
We used a mix of metric and SAE, and I highly suggest you don't do that.
My experience in the workplace is all metric fasteners and Inch units (It's weird but it works well). So That's what I tried to do for my team, which lead to much confusion.
Get 1/4-20, all shapes an sizes,
8-32 and 10-32 are also very common,
Higher loads and bigger interfaces you can go all the way up to 1/2-13 or 5/16-18.
Also, don't forget rivets. They held together ~60% of our robot and are nice for tough to reach places (in terms of getting wrenches in tight places)
We used aluminum and steel 3/16" and 1/8" rivets. Aluminum for light loads, steel for higher loads.