cameras are fitted with 1/4-20 UNC threads. Larger, professional cameras and lenses may be fitted with 3/8-16 UNC threads, plus a removable 1/4-20 UNC adapter, allowing them to be mounted on a tripod using either standard. Historically, The Royal Photographic Society recommended the thread standard for attaching older cameras to tripods was 3/16-24 BSW (3/16 inch nominal diameter, 24 threads per inch), or 1/4-20 BSW for smaller cameras and 3/8-16 BSW for larger cameras and pan/tilt heads. In this application, the BSW and UNC thread profiles are similar enough that one can mount a modern camera on a legacy tripod and vice versa. The UNC threads are a 60-degree angle and flattened, whereas the BSW are a 55-degree angle and rounded crest. However, at least one English manufacturer uses No.1 B.A. (British Association) for its tripod mount thread. Variations There are several types of tripods. The least expensive, generally made of aluminum tubing and costing less than US$50, is used primarily for consumer still and video cameras; these generally come with an attached head and rubber feet. The head is very basic, and often not entirely suitable for smooth panning of a camcorder. A common feature, mostly designed for still cameras, allows the head to flip sideways 90 degrees to allow the camera to take pictures in portrait format rather than landscape. Often included is a small pin on the front of the mounting screw that is used to stabilize camcorders. This is not found on the more expensive photographic tripods. More expensive professional tripods are sturdier, stronger, and usually come with no integrated head. The separate heads allow a tripod-head combination to be customized to the photographer's needs. There are expensive carbon fiber tripods, used for applications where the tripod needs to be lightweight. Many tripods, even some relatively inexpensive ones, also include leveling indicators for the legs of the tripod and the head. Many of the more expensive tripods have additional features, such as a reversible center post so that the camera may be mounted between the legs, allowing for shots from low positions, and legs that can open to several different angles. Small tabletop tripods (sometimes called tablepods) are also available, ranging from relatively flimsy models costing less than US$20, to professional models that can cost up to US$800 and can support up to 68 kg (150 lb). They are used in situations where a full sized