Will these hex keys fit standard metric bolts on my car?

These are SAE sizes (measured in inches), so they'll work on SAE fasteners common on domestic and older import vehicles. Check your bolt head size before assuming fit — metric bolts require metric hex keys.

Do the flat heads really prevent rolling?

Yes. Standard round-shaft hex keys roll off benches and into gaps. Flat heads sit stable on any surface, which saves time and frustration when you're juggling multiple tools.

Are these hardened steel or plated?

Construction details aren't specified in the listing — reach out to confirm material hardness and finish if you need that for heavy-duty or specialty work.