QC Lab: Aluminum vs. Steel Ice Screws

Photographer: J Watt Athlete: Aaron Mulkey Location: Cody, WY

QC Lab: Aluminum vs. Steel Ice Screws

Light is right, but steel is real. So, when it comes to ice screws, what’s the deal? In this QC Lab, Will Gadd and Matt Berry thread their way to the source of truth when it comes to aluminum vs. steel ice screws.

WEDNESDAY, DECEMBER 20, 2023

This is the 3rd installment in the QC lab series on ice screws and will continue the discussion on screw placements and the performance differences between aluminum and steel screws. If you have not read the first two articles you can find them here:

SCREWTRUSION

REBORING OLD ICE SCREW HOLES

Aluminum is Lighter than Steel

When aluminum ice screws first came onto the scene, the attraction of a lighter weight rack caused many climbers to fully switch over. The weight savings spread across a full rack of 14 screws can be upwards of 800 grams. That is serious weight, especially when it’s hanging off your harness on a steep and technical lead, or on your back for a five-hour approach.

Ultimately this means you could bring more food, more gear, or that huge belay parka, all of which may lead to more success and less suffering. But, other than weight, what are the other performance differences between aluminum and steel ice screws?

Both aluminum and steel ice screws, 13cm or longer, are CE certified and meet the EN 568:2015 10kN (2248 lbf) radial strength requirement. Although the stubby 10cm steel ice screws are not CE certified, they also meet the 10kN radial strength requirement. To put this in perspective, let’s imagine your friend Ken weighs 225lbs when loaded up with all his kit. A well-placed ice screw is rated to hold 10 Kens. It is hard to generate that much force in most real-world climbing scenarios.

Ice screws themselves are very strong, but they rely on the support of the surrounding ice which can be highly variable, especially at the surface. In a textbook placement, with the screw placed at a slightly positive angle (tip higher than the hanger) and the hanger flush to the ice, an applied load will stress the ice surrounding the screw and eventually cause the ice to fail. The surface ice will fracture roughly 3 – 5 centimeters deep surrounding the body of the screw. Once this occurs, the exposed section of the screw body becomes cantilevered and is no longer supported by ice. The now cantilevered screw body, unable to support the load alone, will begin to bend until the hanger is levered off the head, the screw body fails, or the screw pulls out of the ice.

Material Properties

Anyone who has climbed enough ice knows that not all ice is created equal, and you must often excavate good placements. However, sometimes this can be extremely difficult. A lot of the ice we climb isn’t perfect, nor is our judgement of ice quality. As mentioned in the QC Lab article on "Screwtrusion" if you unintentionally or knowingly place a screw in marginal ice (bad idea but happens sometimes) then a steel screw may be safer as it can handle higher peak loads in the event of “screwtrusion”.

As the ice screw is only as strong as the surrounding ice, placing a screw into less than perfect ice may cause the ice to break down and cone out at much lower loads which leads to an unsupported and cantilevered screw body. This is where the material and geometry make a significant difference.

Without getting too in the weeds, steel has higher ductility and toughness than the heat-treated aluminum used for ice screws. This basically just means that the steel screws can and do bend/deform more than aluminum screws before failure.

Design Priorities

This doesn’t tell the whole story though. Geometry and design priorities play a huge role in this discussion. When Black Diamond designed the steel Express ice screw many moons ago, the priority was to make a robust and durable work horse. Whereas the aluminum BD Ultralight (UL) ice screws were designed to be just that … ultralight. Both ice screw designs meet the 10kN strength requirements of course, but the design priorities are different—right tool for the job sort of thing.

One obvious example of the geometry differences is the the diameter of the screw bodies. As aluminum is a weaker material, the diameter of the UL ice screw is larger to maintain the strength required to pass the CE requirements. The larger diameter can be an advantage when placingrebored screws. It can also make it easier to line up the holes when drilling naked threads and the larger diameter holes make it less likely that the rope will get stuck when pulling your rope.

Real WorldIt is our responsibility as climbers to choose the best tools for the job and know the limitations of our equipment.

Many people here at BD, including myself and athletes like Will Gadd, use a mixture of aluminum and steel ice screws depending on the objective. This way you can make use of the advantages both models offer. Reboring? Break out the aluminum ice screw with the larger outside diameter. Drilling threads with your 23cm screw? Bring the aluminum screw to make lining up those holes easier and save the weight. Heading out for a glacier walk? Bring those aluminum screws and save some weight. Heading out on a remote backcountry mission where weight is king? Aluminums all the way.

Dealing with a bunch of questionable ice? Break out that steel screw to increase your margins or better yet, ask yourself if climbing the route is worth it. Knowing when to back off rather than risking a fall onto marginal gear is crucial for staying safe in the mountains.