How are tie rods, turnbuckles, and clevises configured?

Tie rods, clevises, and turnbuckles are an important part of many architectural designs. Canopy supports, structural steel bracing, and walkway hangers are a few of the applications that use these assemblies. The unique configuration allows for field adjustments in both length and tension.

Adjustment
Adjustments are possible by threading opposing ends of the rod right hand (RH) and left hand (LH). Another alternative is to provide two clevises threaded RH and use a turnbuckle in the middle that has RH and LH threads. The assembly length and tension is adjusted by rotating the turnbuckle. Both options allow the assembly to be installed and easily adjusted in place.

Grip
The grip on a clevis refers the distance between the legs. This is the area that will be placed over the plate and held by a pin. Generally, the grip size is calculated by the material thickness plus ¼”. Keep in mind the minimum grip is ¾” for #2 through #5 clevises and 1” for #6 and #7.



Pin
Clevis pins are available headed or smooth and are generally secured with a cotter pin connection. In some applications an ASTM A325 structural bolt can also be used to connect the clevis to the structure. Refer to the Diameter of Pin in Inches chart on the clevis page for the appropriate pin dimensions. This chart is designed so that the pin will surpass the matching rod strength.

Galvanizing
Hot-dip galvanized clevises and turnbuckles are available. It is crucial for correct fit that the clevises and turnbuckles are tapped oversize to account for the additional thickness from zinc on the tie rods. To ensure the proper fit Portland Bolt assembles all parts prior to shipping.

Common Layouts
Tie Rod with Two Clevises and a Turnbuckle

Tie Rod with Two Clevises Only

These bolts are identical with regard to strength and chemistry. There are very minor differences in the hardness requirements, but the proof load, tensile, and yield strength requirements are the same. From a manufacturing standpoint, we make these bolts using the same raw material and the same heat treating and production methods. Our strength by grade chart gives a detailed comparison.

The difference between these two specifications (A325 and A449) is the diameter range, configuration, and application. A325 bolts are heavy hex head bolts ONLY, and are designed for structural steel connections. They range in diameter from ½” – 1-1/2” inclusive. Due to their application, an A325 structural bolt has a shorter thread length than a typical heavy hex bolt. If you need a bolt with longer threads, ASTM A449 should be used.

ASTM A449 bolts range in diameter from ¼” – 3” inclusive and are far more flexible in their configuration. In other words, A449 bolts can be a headed bolt, a straight rod with threads, or a bend bolt such as a right angle bend foundation bolt.

With regard to availability, A325 bolts are mass produced and far more common in the marketplace than A449 bolts. Therefore, A325 bolts would be immediately available and considerably less expensive than A449 bolts, unless the bolts you are dealing with are exceedingly long in length. Since the thread length on A325 bolts is very short you should make sure they will be adequate for your application. ASTM suggests using A449 in lieu of A325 when a nonstandard thread length is needed. Here is an excerpt from the A325 specification:

This specification is applicable to heavy hex structural bolts only. For bolts of other configurations and thread lengths with similar mechanical properties, see Specification A 449.

For example, a 1” diameter A325 bolt that exists in the marketplace will have 1-3/4” of thread. There is a supplemental requirement in the A325 specification for fully threaded A325-T bolts that are 4 X diameter in length or shorter. There are often 1” diameter fully threaded A325’s that are readily available but they are no longer than 4” in length.

Portland Bolt’s position regarding ASTM specifications are that they are simply guidelines. They provide a buyer with a reasonable expectation as to the product they will receive if they order it to an ASTM specification. However, if the buyer and seller agree to change any portions of the specification, that is acceptable as long as the change is clear and agreed upon by both parties. Therefore, we frequently manufacture A325 bolts with longer thread lengths than “standard”. Since 1” diameter A325 bolts wouldn’t exist “on the shelf” with that nonstandard thread length anyhow (2-3/8”), it would make more sense to spec the bolt to A449 since it would be the proper spec to use and the bolts would need to be manufactured special regardless of which specification you choose.

The theoretical torque values listed on our site are intended as reference point. This chart only covers products with a published friction coefficient.

These terms are often incorrectly used interchangeably. The variations between these fasteners are fairly significant both from a manufacturing perspective and application standpoint. Generally speaking, hex cap screws are used in precise applications like an OEM setting where tight tolerances are required. A hex bolt is often specified when the mechanical properties are more important than dimensional tolerances, like the construction industry. For example, SAE J429 Grade 2 is typically provided as a hex cap screw, whereas ASTM A307-A is a common hex bolt specification.

Below is an overview of some of the specifics these fasteners are required to meet.

Hex cap screws

• Flat washer facing under the head that meet specific tolerances as described under ASME B18.2.1-1996.
• They will usually be manufactured by a cold-heading process (large runs of standard sizes) or turned CNC operation.
• A radius under the head at the shank.
• Body diameter of plus nothing, minus .011″ for an 1-1/4″ diameter fastener.
• Some common fastener specifications unless otherwise specified: ASTM A449 and SAE J429 Grade 2, 5, and 8.

Hex bolts

• A die seam across the bearing surface is permissible.
• The typical bolt is manufactured by hot-forging process.
• Allows a reduced body diameter to be not less than the minimum pitch diameter of the thread.
• Some common fastener specifications unless otherwise specified: ASTM A307-A, A354, and F1554.

This list is not inclusive, but represents some of the differences between these two designations. There is flexibility to use other materials, grades, and bolt standards as agreed by manufacturer and purchaser. So, be cautious when ordering bolts that you make sure to be clear what type your project requires.

Answer: Unfortunately, we have no specific data to answer this question. First, “standard” lag screws that are readily available in the marketplace are ungraded, meaning they are not manufactured to any ASTM specification and have no mechanical requirements. Therefore, it is impossible to determine the strength characteristics of a lag screw unless they are custom manufactured or the specific lot of bolts is tested. Second, the forces that are acting on these lag screws will affect their ability to hold the structure in place. The shear strength of a fastener is approximately 60% of its tensile strength, but this is only an approximation and unless you have graded lag screws, there is no way to determine shear or tensile strengths. Additionally, the type of wood, grain structure, etc. will determine the ability for a lag screw to withstand the forces that are acting against it. Finally, we have no engineers on staff and due to liability issues; we are not in a position to answer these types of questions. We would recommend contacting a structural engineer.

The American Wood Council has more information regarding wood construction and specific lag bolt recommendations. They also have an extensive wood connection calculator.

The problem with ASTM A108, 1018CF is that there are no mechanical requirements and typically the test reports that accompany this steel reflect the chemistry only and not the strength of the steel. Test reports will need to accompany this material that reflect all four of the values listed below, and these values will need to meet the requirements of the F1554 grade 55 specification. If the test reports do not reflect any or all of the required mechanical properties, a sample of the same heat of material will need to be tested by a laboratory to determine if the 1018 material meets all of the criteria.

ASTM F1554 grade 55 has the following mechanical requirements for diameters ¼” – 2”:

• Minimum Yield: 55,000 psi
• Tensile Strength: 75,000 psi – 95,000 psi
• Minimum Elongation: 21%
• Minimum Reduction of Area: 30%

We have found two resources that give theoretical values one could expect 1018 cold finished steel to meet but they are very different. The steel warehouse sources and theoretical values are listed below:

Based on theoretical values reported by Earl M Jorgensen, in theory 1018 CF should meet the requirements of F1554 grade 55, while the theoretical values reported by Pacific Machine and Tool Steel indicate that 1018 CF will not meet the mechanical requirements of F1554 grade 55. The only way to know with 100% certainty is to have the specific heat of steel tested for Yield Strength, Tensile Strength, Elongation, and Reduction of Area.

Our steel inventory includes material certified to meet all the requirements of grade 55. Most of this steel is supplied directly from North American steel mills and rolled specifically to meet the ASTM specifications.

For many years a malleable iron washer has been a common component in heavy timber and marine construction. With a large bearing surface and thick cast design they help prevent the bolt head or nut from pulling through wood connections.

There are two common types of MIW. One style of malleable washer is produced in the United States, while the other is made overseas. The import option is readily available in the marketplace in sizes for bolts from 3/8″ to 1″ in diameter. It has one nail hole and two notches on the outer edge. The domestic washer is similar with two vertical slots on the outside edge, but is missing a nail hole. Both have similar inside and outside dimensions.

Import MIW

Domestic MIW

According to the original patent from 1907 the outer notches were meant to lock the washer from turning against the wood. A chisel is used to bend the metal edge into the wood. To our knowledge, this installation process is rarely used.

Per ASTM A325 section 6.3.1, the rotational capacity test is defined as a test, “that is intended to evaluate the presence of a lubricant, the efficiency of the lubricant, and the compatibility of assemblies as represented by the components selected for testing.” In a 1970 study referenced by the Research Council on Structural Connections (RCSC), it was shown that galvanizing increases the friction between the bolt and nut threads as well as the variability of the torque-induced pretension. A lower required torque value and more consistent results are obtained when lubricated nuts are used as part of the bolt assembly. Rotational capacity testing must show that the galvanized lubricated nut may be rotated from the snug tight condition well in excess of the rotation required for pretensioned installation without stripping. In layman’s terms, the test is required to show that the nut will not gall on the bolt and that the assembly will develop the pretension load desired.

Since, this test requires that each material lot of bolt and nut be tested individually, contractors will typically administer this test on the job site. However, upon request Portland Bolt can perform this test in our facility prior to shipping.

1. Standard A325 Rotational Capacity Procedure

The bolt, nut, washer assembly shall be assembled in to a steel joint so that 3-5 threads are located between the bearing surfaces of the bolt head and nut. The assembly shall be tightened to no less than 10% of the specified proof load. After initial tightening, the nut position shall be marked relative to the bolt and the specified rotation shall be applied. The specified rotation shall be as follows:

• 2/3 rotation (240deg), for bolt lengths that are 4 times the diameter or less.
• 1 rotation (360deg), for bolt lengths that are over 4 times diameter but no more than 8x.
• 1-1/6 rotation (420deg), for bolt lengths that are greater than 8 times diameter.
• For lengths over 12 times the diameter, the test is not applicable.

After the tightening rotation has been applied, the assembly shall be taken apart and examined for compliance. The assembly fails to pass if any of the following occur:

• Inability to install the assembly to the nut rotation specified.
• Inability to remove the nut after installing the the specified rotation
• Shear failure of the threads as determined by visual examination following removal.
• Torsional or tension failure of the bolt. Elongation of the bolt, between the nut and bolt head is to be expected and should not be classified as a failure.

2. Department of Transportation (DOT)/AASHTO Rotational Capacity Procedure

• 2/3 rotation (240deg), for bolt lengths that are 4 times the diameter or less.
• 1 rotation (360deg), for bolt lengths that are over 4 times diameter but no more than 8x.
• 1-1/6 rotation (420deg), for bolt lengths that are greater than 8 times diameter.

1. Bridge Rotational Capacity
2. Standard
3. Federal Highway Administration

Referencing Specifications

• Procedures for Performing Rotational Capacity Test - United States Department of Transportation
• ASTM A325 10.2 - Testing
• ASTM Work Item WK15535 Test Methods for Rotational Capacity Testing of Plain or Coated Bolt, Nut and Washer Assemblies

Although A307 grade C and F1554 grade 36 are virtually identical, there are some subtle yet very important differences. The ASTM F1554 specification was introduced in 1994 and covers anchor bolts designed to anchor structural supports to concrete foundations. F1554 grade 36 is manufactured from low carbon steel just like ASTM A307 grade C was but in addition to being a bent or straight anchor bolt, can also be a headed bolt that is embedded in concrete and used for anchoring purposes. Most commercially available all thread rod that meets ASTM A307 and is used for anchor bolts will not meet ASTM F1554 grade 36. Additionally, imported A307 hex bolts that are commonly embedded in concrete and used as anchor bolts will not meet F1554 grade 36. However, many fastener distributors and even some manufacturers who do not have a thorough understanding of the differences between ASTM A307 grade C and F1554 grade 36 continue to provide A307 bolts believing they will cross-certify to ASTM F1554 grade 36 which is simply not the case in most instances. It is important to be aware of the differences between these two specifications to limit exposure to unnecessary liability.