7/16ths connecting rod bolts ..

[rubbinisracing]

Adding boron to steel alloys is an inexpensive and potentially dangerous method of achieving higher tensile strength. Boron is not allowed in either grade 5 or grade 8 fasteners according to SAE. Fasteners containing boron must be marked Gr 5.2 or 8.2 on diameters under 1-1/2". Cap screws containing boron are prone to stress-relaxation failure which can be increased when used in high temperature cyclic environments.

Proper knurling should not weaken the clamp load as long as the fillet radius (where head meets shank)is not damaged during the upset.