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)
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
NPT Tap Drill Sizes When tapping NPT threads, the drill size determines the minor diameter of the internal thread. Because NPT threads are tapered, the drill creates a straight hole that the tapered tap gradually engages — you’ll get full threads near the entrance and partial threads at depth. NPT Size TPI Tap Drill (in) … Read more
What is NPT? NPT (National Pipe Thread) is the US standard for tapered pipe threads. The taper is 1°47′ (3/4 inch per foot), which means the threads wedge tighter as you screw them together — creating a seal. NPT threads require thread sealant (Teflon tape or pipe dope) for a leak-free connection. NPT vs. NPTF: … Read more
Matching Nut Grades to Bolt Grades Using the wrong nut with a high-strength bolt is a surprisingly common mistake — and it’s dangerous. A Grade 5 nut on a Grade 8 bolt will strip the nut threads before the bolt reaches its rated clamp load. Always match (or exceed) the nut grade to the bolt … Read more
How to Identify a Hex Bolt’s Grade Every hex bolt has markings on its head that tell you its material grade and mechanical properties. Those radial lines, numbers, and letters aren’t decorative — they’re a specification. Knowing how to read them means you can verify the right bolt is in the right application without pulling … Read more
Standard Flat Washer Sizes Flat washers distribute load under a bolt head or nut, protect the surface from damage, and span oversized or slotted holes. The two common types in the US are: Type A (Narrow) — general purpose, standard series Type B (Wide) — larger OD for better load distribution on soft materials Dimensions … Read more
Standard Hex Nut Sizes These are the basic dimensions for standard hex nuts per ASME B18.2.2. The “width across flats” is what you need for wrench/socket sizing. Nominal Size Threads/in (UNC) Width Across Flats (in) Width Across Corners (in) Height (in) 1/4″ 20 7/16 0.505 7/32 5/16″ 18 1/2 0.577 17/64 3/8″ 16 9/16 0.650 … Read more