Screws and Nuts – How to Choose the Right Fasteners

Understanding metric thread designations

A designation like M12x1.25 on products such as Matica točka M12x1.25 ključ 17 konus FEBI defines the diameter and thread pitch. The number after M indicates the outer diameter in millimeters, while the second number shows the distance between threads. Standard pitch for M12 is 1.75mm, while 1.25mm denotes a fine thread that provides a more secure connection.

Strength grades in screws

Markings of 8.8, 10.9 or 12.9 on the screw head indicate its tensile strength and yield point. Grade 8.8 is most common for general use, while 10.9 and 12.9 are employed in high-load applications in mechanical engineering and automotive industry. Higher numbers mean greater load capacity but also higher cost.

Drive head types

Hex socket (Allen) screws allow higher tightening torque than traditional cross-head types, making them ideal for precision assemblies. Phillips and Pozidriv are standard for wood and interior applications. Torx heads prevent tool slippage and are often used in security applications. Brands like SPAX and WURTH offer specialized drive systems for different materials.

Materials and corrosion protection

Zinc-plated screws provide basic protection for indoor use, while A2 stainless steel (AISI 304) withstands moisture and moderate corrosion. Marine and chemical applications require A4 stainless (AISI 316) with molybdenum addition. Black oxide screws are inexpensive but not moisture-resistant and should only be used indoors.

Lock nuts and washers

Self-locking nuts with nylon inserts prevent loosening due to vibrations, which is critical in machinery and vehicles. Spring washers (Nord Lock) distribute load and additionally secure the joint. For high temperatures, use metal lock nuts or deformed thread nuts instead of plastic inserts.

Application and selection for different materials

For wood fastening, use screws with coarser threads and self-drilling points that don't require pre-drilling. Concrete and brick require plastic anchors (dowels) with appropriate load capacity – brands like FISCHER offer a wide range of solutions. For metal, use machine screws with fine threads and matching nuts, and for thin sheet metal, self-tapping screws with threads extending to the head.

Selection and Pricing

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