General Fastener Knowledge
What is thread pitch?
Thread pitch is the distance between the crest of one thread to the crest of the next, measured in millimeters for metric fasteners.
How do I choose the right fastener?
Choosing the right fastener depends on four key factors: the environmental conditions (corrosion), the mechanical load (tensile/shear strength), the joint design (clearance, vibration), and the base materials being joined.
What is the difference between a bolt and a screw?
Traditionally, a bolt is designed to pass through unthreaded holes and is secured with a nut. A screw is designed to be threaded into a tapped hole in the material itself.
What does 'Grade' mean in fasteners?
Grade (or Property Class) refers to the mechanical strength of the fastener, specifically its tensile and yield strength. Higher numbers (e.g., 10.9 vs 4.6) indicate a stronger, harder metal.
What is galling?
Galling is a form of cold-welding where the threads of a stainless steel bolt and nut seize together under pressure during installation. It can be prevented by using a lubricant or anti-seize compound.
Materials & Metallurgy
What is SS304?
SS304 (also known as A2) is the most common austenitic stainless steel, containing 18% chromium and 8% nickel. It offers excellent general corrosion resistance.
What is SS316?
SS316 (also known as A4) is a premium marine-grade stainless steel that adds 2-3% Molybdenum to the 18/8 mix, vastly improving its resistance to pitting corrosion from chlorides (salt).
What is Duplex Steel?
Duplex steel has a mixed microstructure of austenite and ferrite (50/50). This unique structure gives it double the yield strength of SS316 and exceptional resistance to stress corrosion cracking.
Why use Titanium fasteners?
Titanium fasteners offer the strength of high-tensile steel but weigh about 45% less. They also possess supreme corrosion resistance, especially in marine and aerospace environments.
What is the difference between Hot Dip Galvanized and Zinc Plated?
Zinc plating is a thin electroplated layer suitable for indoor use. Hot Dip Galvanizing (HDG) involves dipping the fastener in molten zinc, creating a much thicker, rugged layer intended for decades of outdoor weather exposure.
Standards & Specifications
What is DIN933?
DIN 933 is the German standard (Deutsches Institut für Normung) specifying the dimensions for hexagon head bolts that are fully threaded up to the head.
What is DIN931?
DIN 931 specifies hexagon head bolts that are partially threaded, featuring an unthreaded shank designed to absorb shear forces.
What is ASTM A193?
ASTM A193 is an American standard covering alloy steel and stainless steel bolting materials (studs, bolts) specifically designed for high-temperature or high-pressure service.
What is the ISO equivalent of DIN 933?
ISO 4017 is the modern international equivalent to the DIN 933 standard for fully threaded hexagon head screws.
Are metric and imperial fasteners interchangeable?
No. Never attempt to force an imperial nut onto a metric bolt (or vice versa). The thread angles and pitches are completely different, and doing so will destroy the threads and cause joint failure.
Applications & Industries
Where are SS316 bolts used?
SS316 bolts are used in environments exposed to chlorides and harsh chemicals, including coastal infrastructure, boats, pharmaceutical plants, and chemical processing facilities.
What fasteners are used in solar panels?
Solar installations typically use SS304 T-bolts and serrated flange nuts for the aluminum mounting rails to prevent galvanic corrosion and ensure a 25-year lifespan.
What are High Tensile bolts used for?
High-tensile bolts (Grades 8.8, 10.9, 12.9) are used in heavy engineering, structural steel buildings, bridges, and automotive engines where immense load-bearing capacity is required.
What is the best fastener for extreme heat?
For extreme heat (up to 2000°F), specialized nickel-based superalloys like Inconel 718 or Hastelloy are required. For standard power plant steam lines, ASTM A193 B16 is common.