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The Hi-Lo screw is easily distinguishable from any other screw due to the characteristic alternation of the thread between high (high) and low (low). It was one of the first screws designed specifically for plastics, especially for very soft materials such as nylon, moplen and the like. The highest thread at 30 ° is the one in charge of ensuring the tightness of the screw in the plastic material, while the smaller one should serve to create a blocking action of the screw by virtue of the different angle at 60 °. In practice, the product behaves like the double-principle rapid-fix "cousin" used in the wood sector: the idea for a screw with similar sealing characteristics, but on plastic materials, developed from the latter. Just like its like, the critical points of this article are varied and should be considered more often in the design phase, so that this screw can be used on a broader spectrum in a much more conscious way as it happens for Plastic-Fix (art. 105 and derivatives). Analyzing the difficulties of the screw, for example, in our experience we have had to deal with plastic products whose pre-hole being too large (this due to the needs of molding and blowing of the plastic) did not allow the lower thread of the screw to comply with the locking action and / or in any case not to have any grip on the material. In fact, by working only one thread, the tightness of the screw is not as it was originally thought. A second case concerns the size of the head which, with the same nominal diameter of the stem, is far less than any other type of product for plastics: the most striking example is found in the 3.5mm diameter screw whose head has a diameter of 5.6mm and with cross 1 instead of 7mm and with cross 2 as in all the others. An apparent strength of the product could be seen in the double step that allows a faster screwing than a normal screw for plastic: unfortunately this value becomes negative when looking at the tightness of the product with the same tightening torque.
The pros and cons of Hi-Lo are these, but not only: for this reason we always recommend contacting the office for more comprehensive and targeted advice.The half-round head with the fake washer favors a wider sealing surface, while the low profile and without edges makes them particularly suitable for "visible" applications.

The length of the screw is measured from the tip to the underhead.