Will these fit my current valve stems?

Yes — these thread onto standard metric valve stems. If you're running aftermarket wheels with custom stems, test-fit one cap before installing all four to confirm compatibility.

Can I remove these by hand or do I need a tool?

The knurled grip is designed for hand removal. You won't need pliers or a wrench — the texture gives you enough friction to unscrew them with your fingers.

Do these lock or just screw on?

They screw on hand-tight. The grip surface helps keep them seated, but they are not a locking cap — normal thread tension holds them in place.