[Rick Parker]

Nothing. Use ARP black oxide, or their stainless in non critical applications, or to reduce expense, plated grade 5 or 8.

Side note:
Various authorities advise against using Grade 8 bolts in a shear applications, because they are very brittle and can fracture before deforming.

Consider bolts in critical applications such as suspension mounts and pivots and some steering components as maintainence items and replace them on a regular schedule. They have an anticipated life expectancy.

At the Nor Cal Mini Nats last month, a rear lower suspension link pivot bolt fractured on Gordon Gimbels Lotus/Ford allowing a huge toe change in the LR tire at about 80 MPH. Fortunately the driver was able to keep it off the wall, without a lot of damage, but it could have been disasterous.