Micro Wallnuts are small alloy nuts that offer greater surface contact area than the equivalent brass nut - an important consideration in softer rock.
DMM's alloy micros are machined from 7000 series aluminium. They incorporate a machined inset radius that both improves strengths and protects the wires.
DMM make these nuts from the harder 7000 series alloys because they must be able to resist high shear forces.
There is a common misunderstanding about small nuts that goes 'micro brassies are stronger and better than alloy micros'. Micro wires virtually always break at the wire loop where it joins the carabiner and the defining factor here is the wire diameter and wire diameter is quite constant for a given head size. It is really a visual issue - an alloy nut looks bigger than an equivalent brass nut and so there is an expectation that it will be stronger.
In reality it is this extra surface area that makes micro alloy nuts so useful - any load is spread over a wider area and reduces the chance of the nut being pulled through the placement.
Thus both brass micros and alloy micros have their place - brass micros will fit smaller placements, but if they fit then the small alloy nuts spread the load better. Place them in clusters, use screamers/ripstops, back them up as soon as possible and if you do fall get your belayer to make the catch as soft as possible.
Small nuts often have two strength ratings on them; this is because the nuts have to be tested in all orientations. Thus the smaller figure will be the rating on the narrow side and the larger figure when placed normally, with the wider face in contact with the rock.
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