Do these lug nuts work with aftermarket wheels, or do I need the adapter?

The adapter is included to handle fitment variations. Test-fit your wheels with the standard nuts first — if there's a gap or seating issue, the adapter fills that space. Most aftermarket wheels thread directly without it.

Will these stay tight after installation, or do I need thread-locking compound?

Standard lug nuts rely on proper torque and re-torque after 50 miles of driving. Thread locker is not required, but some drivers use it as insurance on track cars. Stick to your vehicle's service manual for torque spec and check tightness periodically.

Can I mix these with my existing lug nuts, or should I replace all four?

Replace all four (or all five on trucks) with the same set to keep tension balanced across the wheel. Mixing fastener styles or materials can cause uneven seating and vibration.