Vertical caving terminology and methods > Personal SRT gear
The horizontal metal bars of a rack that are used to create friction against the rope. These wear down over time, and need to be replaced. They are generally made of either aluminium or stainless steel. The aluminium bars wear down much faster and need to be replaced sooner, but are lighter weight, give a much smoother descent, and dissipate heat better. The wear eventually becomes deep enough that the groove of one bar intersects the groove of an opposing bar, reducing the friction, so they are usually replaced when worn half way through. When an aluminium bar becomes worn down to the point that it fails (normally somewhere beyond 2 thirds worn through), it usually fails safely, bending so that it traps the rope, preventing movement. Even if a bar were to fail completely and somehow fall off, the rack would continue to function, with one less bar and little less friction than normal, so this is less catastrophic than a failure of most other descenders. However, users should replace their rack bars before they become too badly worn, and the exact amount will depend on the rack, and the weight of the user. The steel bars are usually so heavy that they are either made hollow, or half-round and hollow, which also helps dissipate heat better. Hollow bars wear out faster than solid bars (but usually much more slowly than with solid aluminium bars), and when they fail, they do so leaving a sharp metal edge next to the rope. Steel bars often get so hot that burns are a significant risk. Bars usually hinge off the rack at one end, and have a clip to hold on to the rack at the other end. Bars often have a groove to guide the rope into the middle of the bar, to avoid wearing down the rack frame. Sometimes, a rack will use one or more hyper bars.
<< Rack, brake bar rack ("rappel rack" in USA) | Hyper bar, tie-off bar, lock-off bar >>
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