You know when you change the wheels on your quad skate? You are using the self-locking nuts. We explain what they are and why it is important to keep them under control.
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What are self-locking nuts?
All skaters need to disassemble from time to time the wheels of their skates: sometimes to clean the bearings, in other cases to replace worn wheels, or to install wheels with hardness suitable for certain surfaces. In these cases, in quad skates (that is, the classic skates equipped with two pairs of wheels side by side), a small but fundamental component must be considered: it is the so-called self-locking nut -an example is shown in the figure below-.
What are self-locking nuts for?
The main purpose of self-locking nuts is to hold each skate wheel in its place, on the drive shaft of the respective truck. To this purpose, each nut must be suitably tightened during installation in such a way as to insist with a slight pressure on the external bearing of the considered wheel. For this purpose, as is known, the drive shafts have ends suitably threaded. However, it should be borne in mind that the system in question is not static: the part of the bearing on which the nut rests could rotate, especially in the case where the bearings should be dirty, and moreover the skate is subject to vibrations and bumps. Under these conditions, a standard nut could loosen, creating freeplay or, in extreme cases, leading to the loss of a wheel: the latter event must be absolutely avoided, as it is extremely risky for the safety of the skater. Even a partial loosening, in any case, involves risks - such as possible loss of control-, so it is essential to prevent the nut in question from being able to accidentally become loose. This is where self-locking nuts come into play. Observing the previous figure, which shows a brand new self-locking nut, you notice that, in the upper part of the component, there is a ring of plastic material, frequently nylon, which in this case is colored blue -but there are variants of different colors on the market, depending on the choice of the manufacturer, without particular technical significance-. The nut self-locking mechanism works like this: when you screw in the nut, the ring in plastic material is deformed by the thread of the axle, adapting to the same. In fact, its internal diameter is slightly smaller than the outside diameter of the threaded part -technically, it is close to so-called diameter of the core of the thread-. The nylon then deforms into permanent way to accommodate the thread, but at the same time tends to apply some pressure on the thread itself. This causes the onset of frictional forces between the plastic material and the thread of the axle, which are the origin of the self-locking function of the nut. It is therefore normal for the self-locking nut to be a little "harder" the first time it is tightened with respect to the subsequent disassembly and reassembly operations.When should I replace the self-locking nuts?
The main problem of self-locking nuts made on the basis of exposed principle -almost all of the nuts used in the sector skating are of this type-, is that after a certain number of cycles of assembly and disassembly, the nylon element tends to lose its properties characteristics, resulting more and more "slack" -for the more technical: the torque tightening and loosening gradually decreases-. Therefore, the nut in question becomes more and more like a standard nut, up to a point at which system security is compromised. It's very common to observe skaters using self-locking nuts which are fully "exhausted", first of all putting at risk their own physical safety and, in secondly, the integrity of their equipment. For this reason, it is very important to verify, at least in a qualitative way, the efficiency of the self-locking nuts: run the exposed risks for a few dolars -that is the cost of replacing the entire set of nuts- hardly can be considered a wise option! But what is the criterion to follow to decide when the Is it time to replace the self-locking nuts on your skates? There isn't one fixed rule, the best thing is to use common sense. Anyway, in if in doubt, it is better to replace the whole set of nuts (it is not good practice use a mix of old and new nuts): the “better safe than sorry” expression certainly makes sense. We can say for sure that, if it turns out possible to unscrew a self-locking nut simply with your fingers, the risk is high! This condition, which to some might seem a bit extreme, in it is actually quite common, for example in skatres used by young people who practice some sports, such as quad figure skating, roller hockey, etc. The point is that in these sports, the substitution of the wheels is a frequent procedure, so that frequently check the nuts status is a must, as their wear tends to be quite quick. For similar reasons, we recommend checking the status of the nuts right away when buying a used skate. Out of order nuts should be disposed, as they cannot be reconditioned, nor -seen the cost- that would make sense.A technical note
Finally, some technical information. The self-locking nuts used in many skating sectors, are of the M7 dimension, for 7 mm axles: in reality these components are not easy to find on the market (e.g. in hardware stores are rarely found), so you are often forced to buy them up from skating equipment dealers. In some cases, 8 mm axles are used, and the relative M8 nuts are rather common. The color of the finish of the nut -metallic gray, gold, colored- or of the plastic ring does not affect the properties of the component; the materials with which it was built, yes. In fact, there are nuts on the market of poor quality, especially with regards to the locking-ring plastic material, which are not able to guarantee acceptable durations. Once again, save a few bucks buying these items from unreliable suppliers could be a bad choice. There are not many alternatives on the market, especially in consideration of the type of use (several cycles of assembly/disassembly): although different types of nuts are available resistant to accidental unscrewing, they are more suitable for one-shot applications, in which the tightening is carried out once. And, by the way, the nuts of the type described above have proven to be reliable and economical in the roller sports sector, as long as the rules dictated by the good sense are followed.Have fun, skate safe!