Will this work with my factory roof rails, or do I need a full roof rack system?

This cross bar mounts directly to your OEM rails — it's a standalone addition, not a complete system. If your 4Runner came with factory rails, you're set to mount this bar and add cargo carriers on top.

Do I need to drill into my roof?

No drilling required. The cross bar connects at factory mounting points on your existing rails, so your roof stays completely untouched.

What hardware do I need to install this?

Hardware specifics depend on your rail attachment method — confirm your rail design before purchase. Standard automotive fasteners (bolts, washers, lock nuts) typically work; refer to your vehicle's service manual for torque specs if needed.