This 4 piece set of Possbay valve caps is made from aluminum alloy and has an internal rubber ring for weather protection. What I liked most about these Possbay valve caps: - The quality. These valve caps are superior in quality to the standard valve caps found on most tires. - Easy to install. Whether you tighten these valve caps by hand or with the included Allen wrench, it only takes a few minutes to improve the look and protect your current valve caps. If you've invested in good tires or rims, it would almost be an insult to leave cheap valve caps on your tire stems. These Possbay valve covers complete the look of those who take care of their car. Security. Because this set can be tightened with a hex wrench, removing by hand is much more difficult. It also means these caps are far less likely to pop out when you hit a pothole than the competition. What I liked least about these Possbay valve caps: - The price. This set is slightly more expensive than the competition, although this set adds a bit of security not typically offered at lower prices. - Distance. If you tighten those valve caps with a wrench and have to take them off to add air, you'll be uncomfortable when you realize you don't have a hex wrench. - Install an aesthetically pleasing and safe way to upgrade standard valve caps. They're a bit more expensive compared to the competition and can be a hassle to remove, but I think these trade-offs are worth it for what you get. 4.0 out of 5.0.