On: United finds loose bolts on plug doors during 737 ...

[serf]

a good machinists handbook will give you torque specs that take into account fastener size, material, and thread-locking style.[0]

mine is much older than linked version, but i doubt they'd revise that whole section out of it.

[0]: https://www.amazon.com/Machinerys-Handbook-Toolbox-Erik-Ober...