No, externally threaded fasteners should not be “chased”. Chasing threads is a term used to describe re-cutting threads after galvanizing to remove excess zinc gained during the galvanizing process. Reworking the threads can possibly remove the zinc coating and eliminate the corrosion protection of the threaded portion of the fastener. Chasing, if not performed with extreme precision, can also remove additional steel from the threaded portion of the fastener resulting in threads that are undersized and out of tolerance.

ASTM F2329 is a relatively new specification that covers galvanized fasteners and supersedes A153. This specification (5.4.1) clearly prohibits the alterations of threads after galvanizing stating, “Fasteners that have been hot-dip galvanized shall not be further altered (such as subjected to a cutting, rolling, finishing-tool operation) by the galvanizer unless specifically authorized in writing…”

Portland Bolt’s custom galvanizing system is specifically designed for threaded fasteners and uses centrifugal force to clean the threads. After parts are removed from the galvanizing tank they are spun immediately following using a high-speed spinner. This process creates high quality galvanized threads and trouble-free nut fit. In addition, galvanized nuts are tapped oversize to accommodate the extra 2 – 6 mils of thickness that hot-dip galvanizing adds. The tolerance for tapping nuts is covered under A563.

No, SAE only covers bolts up to and including 1½” diameter. SAE J429 (1999), the specification that includes Grade 2, 5, and 8 fasteners, states, “This SAE standard covers the mechanical and material requirements for inch-series steel bolts, screws, studs, SEMS, and U-bolts used for automotive and related industries in sizes to 1½ in. inclusive.”

When diameters larger than 1½” are required, ASTM specifications should be considered since many cover fasteners larger than 1½” diameter. Generally speaking, for construction applications ASTM is the most appropriate standard. SAE is more commonly specified for automotive, equipment, or machinery applications.

We often see fastener distributors and manufacturers without forging capabilities talking customers into switching from a headed bolt to a rod with a nut since they are unable to provide the forged product that was engineered into the structure. Substituting a nut for a forged head is not limited to anchor bolts, but that is where we see it occur most frequently. Making the decision to switch from a bolt with a forged head to a rod with a nut should always be approved by an engineer to prevent any liability in making such a substitution should a failure of the fasteners occur.

Wedge Testing per ASTM F606

Headed Anchor Bolts

Rod with a Nut

Note: Wedge testing as shown above is required to obtain mechanical properties for most ASTM high strength fasteners. A greater difference was found for high strength fasteners than mild steel fasteners during Portland Bolt in-house testing of headed bolts versus rods with a nut. The reduced cross sectional area at the junction of the nut as compared to a bolt with a forged head caused the fasteners with a nut acting as a bolt head to break at lower strengths than the bolts with forged heads. Additionally, the high strength rods with a nut acting as a head broke just below the nut which would automatically constitute a failure since the wedge test requires the bolt to break either in the body of the bolt or in the threaded portion, not at the junction of the head.

Answer: According to the American Galvanizers Association (AGA) the weight of an item on average will increase about 3.5% from the zinc added during the galvanizing process. However, the AGA goes on to say, “…that figure can vary greatly based on numerous factors. The fabrication’s shape, size, and steel chemistry all play a major role, and other factors like the black weight, the different types of steel that get welded together, and the galvanizing bath chemistry can also have an effect.”

When considering galvanized fasteners this percentage is often lower. For example, the actual increase in the weight of a galvanized 1″ x 10″ A307 hex bolt compared to a plain hex bolt is approximately 0.26%. The zinc thickness requirement for hot-dip galvanizing threaded fasteners is covered by ASTM F2329. This specification states the average minimum coating thickness at 1.7 mils (.0017 in.). Overall the weight increase of fasteners due to zinc from galvanizing is fairly minimal.

Protective Coatings
ASTM recommends that if a protective coating is required for A490 bolts a Zinc/Aluminum Corrosion Protective Coating should be used in accordance with F 1136 Grade 3. This recommendation is based on findings from research conducted by the Industrial Fastener Institute (IFI 144). No other metallic coating is allowed unless authorized by ASTM’s fastener Committee F16. One trade name of this coating is Dacromet.

Weathering Steel
Another option is to specify ASTM A490 Type 3. This fastener is made from weathering steel which is inherently corrosion resistant. However, these fasteners are not as readily available in the marketplace as A490 Type 1.

Consulting a structural engineer involved on the project is always the best solution.

There are two specifying bodies when it comes to fasteners. ASTM (American Society for Testing and Materials) covers primarily bolts and fasteners for construction applications. SAE (Society of Automotive Engineers) covers fasteners for automotive, machinery, and OEM applications.

ASTM A307 grade B is made from a low carbon steel and is a relatively low strength heavy hex bolt or stud specifically intended for cast iron pipe flange connections. ASTM A449 is a medium carbon steel that is heat treated to develop higher strength characteristics than A307 grade B. Whereas A307 grade B is limited by its configuration (heavy hex head bolt or stud) and its application (cast iron flange connections), A449 can be used for general applications and is unlimited in its configuration. In other words, an A449 bolt can be any type of headed bolt, any shape of bent bolt, or straight rods that are fully threaded, have threads on both ends, or have tread on one end only. Grade 5 bolts are covered under SAE guidelines and by nature are a more precision fastener than ASTM bolts. They are virtually identical to ASTM A449 in chemistry and strength, but max out at 1-1/2″ diameter while A449 bolts extend to 3″ diameter.

Answer: Depending on the type of bolt you are using the thread length can vary greatly. There is not an inclusive thread length standard that covers all fasteners. Depending on the applications, manufacturer, and a number of other factors the amount thread may change. It is important to clearly communicate at time of purchase your desired thread lengths on headed bolts in addition to bent anchor bolts and threaded rods. Below is a brief outline of common fasteners and the thread lengths generally found in the marketplace.

Hex / Heavy Hex Bolts
ASME B18.2.1 which covers hex, heavy hex, and square head bolts, states bolts 6″ in length and under have a thread length that is twice the diameter plus 1/4″. Bolts that are longer than 6″ have a thread length of twice the diameter plus 1/2″. For example, a 1/2 x 6 hex bolt will have 1-1/4″ of thread, whereas a 1/2 x 6-1/2 hex bolt will have 1-1/2″ thread. In our experience, most “off the shelf bolts” that are longer than 12″ have 6″ of thread.

Structural Bolts
Structural bolts like ASTM A325 and A490 specify shorter thread lengths since these bolts are used for steel-to-steel connections and the amount of grip length is critical thread lengths are much shorter. A325 heavy hex bolts with the S1 supplement are to be fully threaded. Those with the S1.2 supplement must be marked, “A325 T”.

Carriage Bolts
ASME B18.5 it states that the thread lengths for carriage bolts 6″ in length and under have a thread length that is twice the diameter plus a 1/4″ and bolts longer than 6″ have a thread length of twice the diameter plus 1/2″. However, the import carriage bolts we stock are fully threaded for bolts 6” long and under and 6” of thread for bolts longer than 6”.

Lag Bolts
The minimum thread length shall be equal to one-half the nominal screw length plus 1/2″ or 6”, whichever is less.

Anchor Bolts
For any type of bent bolt or straight rod there are no thread standards. The thread length of anchor bolts change significantly depending on the application, projection from the top of concrete, and a number of other factors. Most structural drawings will outline the exact dimensions of the anchor bolts, including thread length. It is important to remember that anchor rods often specify different thread lengths on each end.

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.