Steel Manufacturing Blog: Keeping it Steel

Grinnell Standards: Clevis and Turnbuckle Rods

Posted on Wed, Mar 25, 2015 @ 10:46 AM

Grinnell Standards are a way of limiting the variables when designing a clevis rod or turnbuckle rod. While clevis rods and turnbuckle rods can be manufactured in any diameter and set of specifications, keeping it simple is always desirable for the structural steel fabricator. The main structural concern is tensile strength. Round bar diameter is the primary feature that controls tensile strength and the remaining components are designed around that.

Turnbuckles are relatively straightforward. The thread pitch is typically standard coarse thread, or UNC. The diameter of the rod controls the turnbuckle diameter. The only remaining issue is Turnbuckle take-up. In the drawing below T represents take-up, or basically the empty space in the middle of the turnbuckle body. Most turnbuckles used for structural steel have a take up (T) of 6” or 12”. The more popular smaller diameter turnbuckles offer a 3”, 4” and 9” take-up also, but their use is limited.

Designing a Clevis or Thornbuckle Rod, Steel Fabrication, Grinnell Standards

Clevises, on the other hand, have more variables and the possible combinations are endless. Each clevis has to be specified for;

    •    Clevis Number (Size)
    •    Thread Diameter
    •    Clevis Pin Hole Diameter
    •    Clevis Grip Width

In the drawings above, clevis number relates to the outer diameter at the open end, i.e. a #CL35 clevis has a diameter of 3-1/2”.

Clevis Rod, Rod Diameter, Grinnell Standards

See the dimensions of all clevises on our website at:
Thread diameter and clevis size are closely related but not directly linked. A #CL30 clevis could be threaded to accept a clevis rod from 1” to 1-3/8” dia.

(4 Options)

Clevis pin hole diameter is between 1/16” and 1/8” wider than the clevis pin itself. Increments are 1/16”. So a # CL30 clevis might have a clevis pin hole anywhere from 1” to 1-3/4” diameter, in 1/16” increments.

(12 options)

Click here to see the chart showing maximum values:
Clevis grip has a range similar to the clevis hole, although not as accurate. A 1-1/2” drill will always drill the same hole. When a blank clevis has the forks adjusted to the desired width, the result is accurate to about 1/16”. Using the same #CL30 clevis,  the maximum grip width is 1-3/4”. In 1/8” increments, the grip can go from 5/8” the 1-3/4”.

(16 Options)

Taking the three options and combining all the different possible measurements, there are 768 possible clevises that can be made from a CL30 blank.

Grinnell Standards
The Grinnell Standards are a set of dimensions that can be used to simplify the decision making process providing there are no unusual demands the application requires.

View the GRINNEL STANDARDS on our website!  Clevis Manufacturing, Steel Fabrications

Using the CL30 again, the chart shows there are 3 clevises in the Grinnell Standard. They are based on the clevis rod diameter. If it was determined, a 1” diameter rod will provide sufficient tensile strength then the other dimensions are dictated as;

  • Clevis Pin Hole = 1-3/16”
  • Clevis Grip Width = 1”
  • Clevis Pin Diameter = 1-1/8”

There is no requirement to use Grinnell Standards. The Steel Supply Company can produce clevis rod and turnbuckle rod assemblies in any dimensions required.

Stainless steel clevis rod assemblies, stainless steel turnbuckle assemblies and stainless steel clevis pins do not follow the Grinnell Standards, but there is no reason the same consistent dimensions cannot be used.


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Note: All load-bearing clevis rod and turnbuckle rod assemblies should be designed by a licensed engineer.


Steel Supply Co. provides a free Turnbuckle Assembly Worksheet & Guide


Tags: Clevis Rods, Hanger Rods, Sag Rods, Turnbuckle Rods