Review on 🔩 4 Pack Universal Tire Valve Stem Caps - Heavy-Duty Stem Covers with Dust Proof O Rubber Seal - Crown Style Design for All-Weather Outdoor Protection - Leak-Proof Air Guard - Lightweight & Durable (Black) by Balthazar Cooper

These are cool little novelties to snap onto valve stems. The crowns themselves are plastic, but the threads appear to be aluminum. I've had them for about a month and a half now (I think) and haven't had any issues and they're all still in place. I even added air and they held up great when taken off.