Threaded joints are probably the most common form of mechanical assembly. They allow for the inexpensive but effective joining of parts. This allows for less expensive manufacturing and easier maintenance, repair or servicing of a finished assembly.
To take advantage of threaded joints, you need to understand was standard sizes of threads exist, what types of bolts and hardware exist and what are the implications of different grades of hardware – in terms of size, mechanical properties, corrosion resistance and fastening strength.
Unified Screw Threads – Fine (UNF)
Unified Screw Threads – Course (UNC)
National Pipe Thread (NPT)
Metric Thread
ACME Thread
Socket Head Cap Screw (SHCS)
Hex Head Cap Screw (HHCS)
Button Head Cap Screw (BHCS)
Imperial Bolt Strength Chart (SAE & ASTM) Standard strength ratings for carbon and alloy steel bolts up to 1″ diameter. These are the grades you’ll encounter on 99% of US engineering drawings. Grade Head Marking Material Proof (psi) Yield (psi) Tensile (psi) SAE Grade 2 No markings Low carbon steel 55,000 57,000 74,000 SAE Grade … Read more
What’s the Difference? Cutting taps and form taps both create internal threads, but they do it in completely different ways — and they require different drill sizes. Confusing the two is one of the most common (and costly) mistakes on a shop floor. Cutting Taps (Chip-Producing) Cutting taps work exactly like you’d expect: they have … Read more
Minimum Thread Engagement How deep does a bolt need to thread into a part before the threads strip? This is one of the most common questions in fastener design — and the answer depends on the relative strength of the bolt and the tapped material. Rule of Thumb Tapped Material Minimum Engagement Recommended Engagement Steel … Read more
Understanding Bolt Preload Bolt preload is the tension (clamping force) induced in a bolt when it’s tightened. This preload is what holds your joint together — not the bolt’s ultimate tensile strength. A properly preloaded joint resists external loads by maintaining clamping force on the parts, preventing slippage and fatigue. Why Preload Matters More Than … Read more
Set Screw Holding Power & Tightening Torque Set screws hold collars, pulleys, gears, and knobs on shafts. Their holding power depends on the point style, material hardness, and seating torque. Under-torqued set screws are the most common cause of components slipping on shafts. Recommended Tightening Torque Set Screw Size Cup Point Torque (in-lbs) Axial Holding … Read more
Bolt Clearance Hole Sizes When a bolt passes through a part without threading into it, the hole needs to be slightly larger than the bolt diameter. How much larger depends on how precisely the holes need to align. US Bolt Clearance Holes Bolt Size Close Fit (in) Normal Fit (in) Loose Fit (in) #4 (0.112) … Read more
How It Works Structural beam analysis determines internal forces, bending moments, and deflections that develop when loads are applied to horizontal structural members. These calculations form the foundation of safe structural design by ensuring beams can support applied loads without failure or excessive deflection. Shear Force (V) represents the internal force tending to cut through … Read more
Standard Bolt Torque Values These are recommended tightening torques for standard dry (unlubricated) bolts. If you’re using lubricant, anti-seize, or plating, reduce torque by 25–30% — lubrication dramatically changes the torque-tension relationship. Grade 5 Bolts — Torque Values Bolt Size TPI (UNC) Clamp Load (lbs) Torque Dry (ft-lbs) Torque Lubed (ft-lbs) 1/4-20 20 2,025 6.3 … Read more
Socket Head Cap Screw (SHCS) Dimensions Socket head cap screws are the go-to fastener for machine design. Their cylindrical head fits into a counterbore, allowing the screw to sit flush with or below the surface — critical when you need clearance for moving parts or a clean look. All dimensions per ASME B18.3: Screw Size … Read more
Metric Hex Bolt Head Dimensions When working with metric fasteners, the wrench size (width across flats) follows a different pattern than US bolts. Here’s the quick reference: Bolt Size Width Across Flats (mm) Width Across Corners (mm) Head Height (mm) M5 8 9.24 3.5 M6 10 11.55 4.0 M8 13 15.01 5.3 M10 16 (or … Read more