Mark the hole accurately then touch the spot you are drilling with a grinder. This will cut through the surface hardening that occurs when the nerfs/bumpers are polished. Any good bit will work. I discovered this trick once I figured out that the second hole, drilled from the inside of the tube was much easier than the first

Pilot point, DeWalt 3/16 cobalt works extremely well on stainless nerf bars. Pilot point is the key.

My son told me about an oil like wax, as you drill the wax melts & lubes the bit

Spindler

I left out my most important tool the "Drill Doctor". In my younger days when my eyes would focus I could sharpen a drill bit by hand and get good results. Now I would be lost without the old "Drill Doctor". I went to the DeWalt add and it said up to 3/8" they simply use a split point drill, which can be ground on the "Drill Doctor". This type point more or less makes the drill act like a pilot drill. The larger bits actually have a pilot drill ground on the tip of the bit and would work great until you needed to sharpen it, then you would be SOL.

Honest Dad himself