Losi XX tool types imperial confusion

[daz75]

I've been using some old tools i got from my dad but most of them are crap so thinking of getting some new ones. The instructions dont say what size hex drivers i need and the screw sizes confuse me as they are all imperial. For example 4-40 3/8" 3/8" is the length, what does 4-40 mean and how does it relate to the size of the drivers as they all say

Inexpensive set with Aluminium machined and anodised handles. Hard bit. Four sizes - 0.050, 1/16, 5/64, 3/32

So would none of those fit the 4-40 3/8?

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