Ice screw

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.

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. Many Titanium ice screws were initially made in the former Soviet Union using Cold War-era missile technology, but were generally too brittle and so the majority of ice screws are now 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. 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, such as the 'snarg' and the 'warthog'. Instead of screwing these into the ice one would pound them in with a hammer from the ice tool, and then screw them out with the pick of an ice axe. The pound-ins have been largely replaced by modern tubular ice screws that are stronger and easier to use, although warthogs are being manufactured in Britain again for use in creating an anchor in frozen turf when no alternative anchor or placement is available, although it is now recommended only as 'marginal' equipment for when no other CE-tested equipment can be placed.

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Wikipedia