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An ice screw is a threaded tubular screw used as a running belay or anchor by climbers on steep ice surface such as steep waterfall ice or alpine ice during ice climbing or crevasse rescue, to hold the climber in the event of a fall, and at belays as anchor points. ==Design== Ice screws may come with one or more of the following: an in-built or separate ratchet mechanism to speed up placement, conical centre-hole to aid removal of ice cores, different lengths, different numbers of cutting teeth, different cutting angles, different surface finishes, and different size clip holes. Price and durability are usually design considerations too, as a usable rack of ice screws will be a significant financial investment for many climbers. Titanium ice screws, often made in the former Soviet Union using Cold War-era missile technology, were generally too brittle and so the majority of ice screws are made of chromoly steel. The strongest and most reliable type of ice screws currently available are the modern tubular ice screws which range in lengths from 10 to 23 cm. The approximate strength rating on a modern tubular ice screw is around 7 kN, and it has been found that short ice screws in good ice hold about 7-8 kN, no matter what the fall factor or configuration is.〔(Beverly and Attaway )〕 The International Climbing and Mountaineering Federation drop test specifies that when multi-pitch lead climbing and the leader has only placed one screw (typically merely clipping one of the anchor screws) before climbing up a couple of meters and falling (a fall factor of 2), the screw must hold.〔()〕 The dynamic ropes used in climbing can mitigate failure of an ice screw by keeping the impact forces low, especially if using a new rope that has not had any previous falls. It is rare that an ice screw fails in fall factors of 1 or less, if placed in good ice. An older type of screw that is rarely used today is a pound-in ice screw. Instead of screwing these into the ice one would pound them in with a mountaineering hammer or a hammer from the ice tool, and then screw them out to remove them. The pound-ins have been largely replaced by modern tubular ice screws that are stronger and easier to use. In the "Rosetta" project, the European Space Agency equipped its lander with multiple ice screws to obtain stability on comet surface, but they failed to hold and the lander bounced a significant distance from the initial landing site. The latest ice screws incorporate replaceable tips, thereby increasing the useful life of the screw and enhancing placements.〔 (E-Climb: Ice Screw Replaceable Tips )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「ice screw」の詳細全文を読む スポンサード リンク
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