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)
Standard Hex Cap Screw Dimensions Hex cap screws (also called hex cap bolts or hex head bolts) are the workhorse fastener of mechanical assembly. This table covers dimensions per ASME B18.2.1 — the data you need for designing bolt holes, counterbores, clearances, and grip lengths. Key Dimensions Explained Width across flats (F) — your wrench/socket … Read more
Metric Tap & Clearance Drill Sizes This table covers standard coarse pitch metric threads (the default — if a drawing says “M10” without specifying pitch, it means M10×1.5 coarse). For each thread size, you get the tap drill (for cutting internal threads) and clearance drill (for a bolt to pass through freely). Thread Pitch (mm) … Read more
UNF Tap Drill Sizes UNF (Unified National Fine) threads have more threads per inch than UNC for the same diameter. They’re stronger in thin-walled parts, provide finer adjustment, and resist vibration loosening better — but they’re less forgiving and easier to cross-thread. Thread Size TPI Tap Drill Decimal (in) 75% Thread Clearance Drill #0-80 80 … Read more
UNC Tap Drill Sizes UNC (Unified National Coarse) is the default thread series in the US. If a drawing says “1/2-13” — that’s UNC. Coarse threads are stronger, more forgiving of dirty conditions, and easier to assemble than fine threads. Thread Size TPI Tap Drill Decimal (in) 75% Thread Clearance Drill #1-64 64 #53 0.0595 … Read more
UNF Thread Specifications UNF (Unified National Fine) threads per ASME B1.1. Fine threads have a larger minor diameter than coarse threads of the same nominal size, which means higher tensile strength and better performance in thin-walled parts. Size TPI Major Ø (in) Pitch Ø (in) Minor Ø (in) Tensile Stress Area (in²) #0-80 80 0.0600 … Read more
UNC Thread Specifications This table gives the basic thread dimensions for UNC (Unified National Coarse) threads per ASME B1.1. These are the numbers you need for thread design, tolerance calculation, and thread gauge verification. Size TPI Major Ø (in) Pitch Ø (in) Minor Ø (in) Tensile Stress Area (in²) #1-64 64 0.0730 0.0629 0.0527 0.00263 … Read more