Air force mechanical aptitude ?

60% of all jobs are reserved to be  chosen during basic, yoy actually have a better shot at getting thre job you want in basic than by MEPS.

now everything is based on how high your Mech score is and are you higher then everyone else who list that job that week in basic

Somebody has to screw the detonator into the bomb and check that it is good to go.  Since it is such delicate work, you want someone with high aptitude to do it.