How To Properly Measure Fasteners

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A precise installation requires clear measurements and an understanding of key engineering terms. Use this guide to correctly identify, measure, and select P1 Manufacturing high-performance fasteners for your application.

1. Length Measurement: UHL vs. OAL

• Standard / Non-Countersunk Bolts: Measured by Underhead Length (UHL) - the distance from the flat bearing surface beneath the bolt head to the extreme tip of the shank.

  
  

• Studs: Measured end-to-end for Overall Length (OAL). Individual sub-measurements track block-side thread engagement, the unthreaded shank, and nut-side active thread length. For studs, specific end styles define the block-side interface: Flat (standard chamfered end) or Dog (a pilot tip or reduced-diameter section). Dog Length refers to the length of this pilot tip, which facilitates easier starting in deep or restricted blind holes.

2. Diameters & Shank Profile

• Major Diameter: The peak-to-peak measurement across the outside thread crests.

  
  

• Minor Diameter: The root-to-root measurement at the bottom trough of the thread groove.

  
  

• Pitch Diameter: The theoretical diameter located halfway between the major and minor diameters where thread width equals space width.

  
  

• Grip Length: The unthreaded shank portion of a bolt body situated between the head bearing surface and the start of the threads.

  
  

• Undercut Shank: A shank engineered with a reduced body diameter, designed to redistribute strain evenly across the entire fastener body and maximize fatigue resistance.

  
  

• J-Form Threads (UNJ): A thread profile featuring an enlarged, smooth radius at the thread root, designed to eliminate sharp stress risers that can initiate fatigue failure. P1 manufacturing utilizes a specialized thread-rolling process to form these threads, inducing compressive residual stress for maximum fatigue resistance.

  
  

3. Thread Pitch & Sizing Standards

• Imperial (SAE / Standard): Specified as Major Diameter - Threads Per Inch (TPI). Example: 3/8-24 indicates a 3/8" major diameter with 24 threads per inch. Within imperial standards, you will encounter two primary thread series: UNJC (Unified National Coarse) for applications requiring greater thread depth in softer materials, and UNJF (Unified National Fine) for high-stress applications requiring higher tensile strength and finer adjustment.

  
  

• Metric: Specified as Major Diameter x Pitch (in mm). Example: M10 x 1.25 indicates a 10 mm major diameter with a 1.25 mm peak-to-peak distance between adjacent threads.

4. Thread Engagement Guidelines

• Load Distribution: Proper thread engagement is critical to ensure the fastener reaches its intended clamp load without stripping the block threads.

  
  

• Steel Blocks: A minimum engagement of 1.5x the fastener diameter is the standard requirement. Because steel is harder than the fastener material, this depth ensures the fastener itself will reach its yield point before the block threads fail.

  
  

• Aluminum/Soft Alloys: A minimum engagement of 2.0x the fastener diameter is required. The additional depth compensates for the lower shear strength of aluminum, preventing thread "shear-out" and ensuring the assembly maintains full integrity.