Thread Flank Angle:
Thinner flank angles on threads (30 degree vs. 48 degree) reduce radial stress on plastic boss and helps to resist strippage
Length of Engagement:
Fasteners should have a minimum of 2.5 times the fastener diameter for length of engagement into the plastic boss. Shorter length engagement will have lower strip out torque and less clamp load
The Boss ID design should have a ½ to 2 degree included draft angle, (+/- ½ degree tolerance is typical) with a lead in similar to the diagram.
Nominal Boss ID:
Calculated at a depth equal to half of the fastener's total length of engagement; In moderately stiff materials, you should start with a hole size that is 75% to 80% thread engagement.
Driver Gun speed
The assembly driver gun should not exceed 600 rpm
Seating and Assembly Torque:
Developed through testing. Assembly torque is normally 70% of the average failure torque.