Trust the Source, Specify ProMoly®.

Plymouth Tube Company produces ProMoly® Seamless Alloy 4130 tubing to conform to MIL-T-6736B and AMS-6360.    ProMoly tubing is superior to plain carbon tubing and exceeds the industry specs for 4130 tubing.

In addition, using ProMoly offers distinct advantages to frame builders.  The consistency of the OD and wall makes setup easier and minimizes set up variation – a distinct advantage during build season.  And proprietary controls of our annealing process offer welders the benefit of a surface finish with minimal decarburization and oxidation, reducing weld area preparation time.  When choosing a tube for your racing application, trust the source of manufacturing excellence with almost 90 years of experience.   Use Plymouth Tube’s race-proven, industry-approved  ProMoly tubing to bring you across the finish line first on race day!

ProMoly® is a registered Trademark of Plymouth Tube Company.


  • Superior to plain carbon tubing
  • Exceeds the industry specs for 4130 tubing
  • Excellent fatigue strength
  • High elongation values
  • More efficient builds, less set-ups due to consistency of the OD and wall
  • Inherent toughness (no weld seam)
  • Predictable, repeatable weldability with minimal distortion

Product Data

OD: .125” – 2.250”

OD Tolerance:  +/- .005″ (up to 1.500″ OD),  to +/- .010″ (above 1.500″ OD)

Wall Range: 0.02″ to 0.250″

Wall Tolerance:  +/- 10% (For ID’s Over .500″) to +/- 15% (for ID’s under .500″)

Specifications: AMS-T-6736A,   AMS-6371, AMS -6360, MIL-T-6736B Quality Assurance Certification:  ISO/IATF 16949:2016

Related Markets

The preferred ChroMoly material for chassis builders, including:

  • Sprint Car
  • Midget
  • Buggy
  • Dirt Track
  • Rally Car
  • Dragster
  • Motorcycle
  • Tractor Pull
  • Formula
  • Funny Car
  • Stock Car
  • Kart
  • Late Model