To measure accurate preload, service load and overload of bolted assemblies

For maximum uniformity, efficiency and reliability in bolted assemblies

For effective research, testing and manufacturing of bolted assemblies

Allowable Loads
Allowable loads for Strainsert Hex Head Cap Screws, as tabulated below, are based on approximately 70% Yield Strength of the threads, in pounds.
Load Capacity Lbs.
Screw Dia. Fine Threads Coarse Threads
1/4 2800 2800
5/16 5400 5000
3/8 7800 7500
7/16 11000 10000
1/2 15000 14000
9/16 20000 18000
5/8 26000 23000
3/4 38000 33500
7/8 52500 46000
1 70000 62000
1-1/8 88000 78000
1-1/4 110000 97000
1-1/2 160000 144000

Each cap screw is calibrated to above indicated load as part of quality control procedure. See calibration section for additional calibration certification.

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Unit of Measure



N/A Steel Alloy (SAE Grade 9), SAE 4140 or equivalent


N/A Rockwell C38 to C42

Ultimate Tensile Strength

N/A 180,000 psi Minimum; (SAE Grade 9)


N/A Class 2A, rolled

Thread Length

N/A 2-diameters + 1/4 inch full threads + 3/16 inch maximum imperfect threads


N/A Zinc Dichromate plated. Corrosion Protection per Federal Spec. QQ P-416 Type II, Class 3


N/A Load & Unload Calibration Load Only Calibration (Standard)

Performance Specs

Gages Type

N/A Metal Foil

Gage Factor (Nominal)

N/A 2.00


N/A ±1% of Allowable Load FS


N/A ±0.1% FS


N/A 350-ohm (Standard) FB: 12V (Maximum)
350-ohm (Standard) QB: 6V (Maximum)
120-ohm FB: 3V (Maximum)

Output Signal (Nominal)

N/A FB:3.5 to 4mV/V
QB:1.3 to 1.5mV/V


N/A Full Bridge Strain Gage Circuit (Standard) Quarter Bridge Strain Gage Circuit

Bridge Resistance (Nominal)

N/A 120 Ω 350 Ω (Standard)

Service Temperature

N/A 150°F (Standard) 300°F (Max.)

General Information

N/A Strainsert fasteners utilize an exclusive internal gaging method (U.S. Patent #2,873,341) to indicate bolt tension due to preload and subsequent service loads with strain gage accuracy. They are the first fasteners to provide a means for accurate, independent inspection of an assembled bolt for preload, thereby enhancing the structural integrity and reliability of both the bolt and the assembly.


  • Measurement of preload induced in fasteners
  • Accurate tightening of fasteners within 1% of induced load
  • Uniform tightening of fasteners in a bolt pattern.