Roller skates can be purchased expressly for indoor or outdoor skating, but many skaters just swap out the wheels and use them for both. Jam skates were originally designed for use in music festivals where there was no pavement to skate on; however, modern versions are able to handle regular ice or concrete well enough for informal use. There are two types of jam skates: platform and pivot. On a platform jam skate, there is a raised metal plate that acts as a footbed. This style is best used for skating around obstacles such as house walls or fences. Pivot jams are identical to normal roller blades except that they have removable wheels that can be replaced with flat objects such as boards or discs. These are useful for when you don't want to cover any distance or when skating on ice. Platform jams may look more expensive than other models, but they are actually cheaper because they don't have bearings or other moving parts that might break down over time. Pivot jams are usually less expensive but require more maintenance. Both types of jams can be used indoors or outdoors, but platform jams are not recommended for outdoor use because they will wear out faster due to the weight of a person standing on them. Jam skates were popular among musicians in the 1970s and '80s.