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

(Ferry Cap Counter-Bored Screws interchangeable with most Socket Head Cap Screws)

Allowable Loads
Allowable loads for Strainsert 12-Point 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 2700 2700
5/16 5400 4800
3/8 8200 7200
7/16 11000 10000
1/2 15000 14000
5/8 25000 22000
3/4 36000 32000
7/8 50000 44000
1 67000 59000
1-1/8 - 74000
1-1/4 - 92000
1-1/2 - 136000

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

For full configuration click Request Information button
Unit of Measure



N/A Steel Alloy, SAE 4140


N/A Rockwell C37 to C43

Ultimate Tensile Strength

N/A 170,000 psi Minimum


N/A Class 3A, rolled to 1” dia.; Class 2A, rolled 1-1/8” dia. & larger.


N/A Black Satin Finish


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


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 mV/V
QB:1.4 mV/V


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

Bridge Resistance

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