I am looking for an industry standard spec that gives recommended torque specs for different screw sizes.
Not that simple... There is not a one-torque-specification that fits all applications.
There are calculated torque values for specific bolts for given applications. For example engine torque specifications for head bolts or main bearings. These are often derived from SAE-Grade Bolts and standards associated for torque. Though using these specifications for any random application can be a serious mistake.
If you have a specific existing application use the torque table specifications provided by the designer, engineer or product manufacturer.
Proper torque ranges are determined by the application and expected loading as well as the bolt strength characteristics. These values are determined by the engineer or designer after analyzing the assembly strength requirements.
What is considered when designing for proper bolt torque.
Static or dynamic loading,
Shear, tension, compression or combined loading applied,
Peak application loading relative to yield strength of internal and external threads,
Failure modes and factor of safety (FOS),
Failure modes include:
Tensile failure of bolt body
Shear failure of both internal the external threads
Tensile failure is derived from the bolt and base materials specifications.
After all of the above and maybe an unknown variable analysis (thermal stress, corrosion, fatigue) is complete the torque can be calculated.
Tell me and I forget. Teach me and I remember. Involve me and I learn.