Many jurisdictions in Asia, Europe, and North America seasonally allow snow tires with metal or ceramic studs to improve grip on packed snow or ice. Such tires are prohibited in other jurisdictions or during warmer months because of the damage they may cause to road surfaces. The metal studs are fabricated by encapsulating a hard pin in a softer material base, sometimes called the "jacket". The pin is often made of tungsten carbide, a very hard high performance ceramic. The softer base is the part that anchors the stud in the rubber of the tire. As the tire wears with use, the softer base wears so that its surface is at about the same level as the rubber, whereas the hard pin wears so that it continues to protrude from the tire. The pin should protrude at least for the tire to function properly. Snow tires do not eliminate skidding on ice and snow, but they greatly reduce risks.