All-Pro Fasteners: keeping you informed, answering your questions, and helping you find the right fastener for the job. Here are some frequently-asked questions (FAQs) we can answer for you.
1. WHY IS A MAXIMUM TENSILE STRENGTH SPECIFIED FOR ASTM A307 – GRADE B?
These bolts are often used in pipe flanges, and to protect the flange, the bolt is designed and manufactured to break before the expensive pipe flange is damaged through overtightening.
Editorial Note: ASTM A307 now requires both a manufacturer’s mark and grade marks on the top of the bolt heads. Grade identification consists of “307A” or “307B” on each bolt produced to meet standard requirements.
2. WHAT DOES ASTM A307 REQUIRE FOR COLD HEADED FASTENERS OTHER THAN THOSE OF THE HEX CONFIGURATION?
The standard requires that these configurations be stress relief annealed to remove cold work effects, particularly at the junction of head to shank. This process is a very important requirement for such products as carriage bolts, for example.
3. WHERE MAY ONE FIND THE DEFINITION OF “ALLOY STEEL” AS DEFINED BY AISI WITHIN ASTM F16 SPECIFICATIONS?
See paragraph 6.1 of ASTM A490. This paragraph includes a Note 4, which defines an alloy steel as follows: “Steel is considered to be alloy, by the American Iron and Steel Institute, when the maximum of the range given for the content of alloying elements exceeds one or more of the following limits: manganese, 1.65%; silicon, 0.60%; copper, 0.60; or in which a definite range or a definite minimum quantity of any of the following elements is specified or required within the limits of the recognized field of constructional alloy steels: aluminum, chromium up to 3.99%, cobalt, columbium, molybdenum, nickel titanium, tungsten, vanadium, zirconium, or any other alloying elements added to obtain a desired alloying effect.”
4. WHAT IS THE ROTATIONAL CAPACITY TEST?
The rotational capacity test is defined in ASTM A325, Paragraph 6.3. It is a test to determine the efficiency of the lubricant required for both hot dipped and mechanically deposited zinc coated nuts. The test involves full size product. The initial tightening of the nut shall produce a load in the bolt not less than 10% of the specified proof load. The nut is then rotated 240 – 420, depending upon bolt length. Upon removal of the nut, there shall be no shear failure of the threads, torsional bolt failure, or other signs of failure.
How many threads should protrude through the nut for full thread engagement? A minimum of two thread pitches should protrude beyond the nut face following tightening to assure full thread engagement.
5. WHY USE COATINGS AND PLATINGS?
Usually coatings and platings are less expensive than employing an upgrade from a basic carbon steel to a premium material such as stainless steel. Coatings or platings may help to improve appearance, control torque tension, minimize thread seizure, and may serve as product identifiers, in addition to simply providing corrosion protection.
6. WHAT ARE THE GENERAL GUIDELINES FOR COATING THICKNESSES?
To ensure thread assemble ability of mating fasteners, the specified thread fit allowance in the inch series, divided by 6, provides the maximum coating thickness.
7. WHAT MAKES CADMIUM A DESIRABLE MATERIAL FOR PLATING?
While there have been many issues involving the environment, safety, and health, the inherent lubricity characteristic of this plating material has never been completely duplicated over a full range of applications. For instance, in salt water, a cadmium coating forms a protective cadmium chloride surface layer which is not sacrificial.
8. WHAT FACTORS CONSUME THE APPLIED TORQUE WHEN TIGHTENING A BOLTED JOINT?
About 90% of the torque applied in tightening a bolt is used to overcome friction – 50% of the torque is consumed by friction of the bearing face of the nut or bolt, whichever surface is rotated; about 40% is consumed by the contact flanks of the threads. The remaining 10% is useful in producing bolt tension.
9. WHAT’S THE CORRECT TORQUE?
This question is frequently asked, but it cannot be reduced to a simple answer or reference table. Many variables determine the correct answer – fastener surface finish, coating, plating, class of screw thread fit, etc. All variables must be taken into account to determine a realistic torque coefficient. Once calculated, check the result in a sample joint to measure clamp load induced from a given applied torque or breaking torque. Then back off that torque setting an appropriate percentage. But remember that induced variances can be Â±20% from a norm.
10. WHY DO BOLTS LOOSEN?
The main reason is insufficient preload, allowing transverse slip of bolt and joint members. Preload, or residual tension, in a tightened bolt means more to assembly strength than actual strength of the fastener, itself. In a joint, a bolt torqued to its proper load level can resist a maximum amount of external load without loosening. Designers can take advantage of this fact to ensure correct bolt loading, and at the same time reduce fastener costs.
FACT: Assembled bolts are tightest when stressed as near as possible to their elastic limit!
11. HOW IS SHEAR STRENGTH OF FASTENERS DETERMINED? WHY DON’T INDUSTRY FASTENER STANDARDS INCLUDE SUCH VALUES?
Common practice for steel fasteners is to assume shear strength will approximate 60% of minimum tensile strength. Published data in commercial (non-aerospace fields) does not offer much guidance on shear strengths for bolts, screws, or studs. The first reason is that the number of components loaded in shear is considerably less than for tension, compression, bending, or torsion.
The primary reason for this lack of direction, however, is the difficulty in obtaining accurate test data. Shear testing inherently involves a number of variables. Therefore, tests are less reproducible than testing for such properties as tensile or yield strength. Most shear testing has been engaged using arbitrary procedures that provide empirical results. The greatest need for shear test data is in structures that are riveted, pinned, or bolted, and also where service stresses are actually in shear. Notable examples are found in the aerospace industry. (A recommended shear test method is provided in ASTM B565.)
12. WHEN A BOLT IS OVERLOADED IN FATIGUE, WHERE CAN I EXPECT FAILURE TO OCCUR?
Three stress-concentration locations lead to most fatigue failures in common bolted joints: 65% of failures – 1st thread to engage the nut; 20% of failures – at thread runout of bolt; 15% of failures – fillet junction of bolt head to shank.
13. WHAT’S THE DIFFERENCE BETWEEN HYDROGEN EMBRITTLEMENT AND STRESS EMBRITTLEMENT?
If you think hydrogen’s detrimental effect on fasteners is just induced from “processing”, think again. It could be the “environment.” Failure mechanisms often viewed as synonymous are stress corrosion cracking, hydrogen embrittlement, and hydrogen-assisted stress corrosion. The reason for this generalization is understandable. Cause and effect similarities outnumber identifiable differences. The reality is that stress corrosion cracking and hydrogen-assisted stress are both corrosion-related. Each causes failure – the actual breaking of the part. But, the fracture is delayed. Sometimes it occurs within hours after load is applied. Sometimes not for months, even years. But, when failure occurs, it’s sudden, with no advance warning. Failures occurring in service can be serious, costly, even catastrophic.
Hydrogen embrittlement is associated with carbon and alloy steel fasteners.
The cause for this embrittlement is the absorption of atomic hydrogen into the fastener’s surface during manufacture and processing – particularly during acid pickling and alkaline cleaning processes prior to plating. Embrittlement can also occur during electroplating, when the deposited metallic coating traps hydrogen against the base metal. If the hydrogen is not diffused out by post-baking, the gas migrates toward points of highest stress concentration when stress is applied. Pressure builds until strength of the base metal is exceeded and minute ruptures occur. Hydrogen is exceptionally mobile. It will quickly penetrate into any newly formed cracks. This pressure/rupture/penetration cycle continues until part failure.
Hydrogen embrittlement is non-corrosion-related. It can be neutralized by proper processing before the fasteners are released for service. And, while hydrogen can be baked out before it embrittles, it’s not possible to bake out the micro cracks once formed. Stress embrittlement is similar to hydrogen embrittlement – with the generalized exception that the presence of offending hydrogen is chemical-reaction induced through the service environment – not because of in-plant processing. An example of this issue can be found when caustic materials (such as soaps, detergents) come in contact with nitrates and silicates. These compounds can chemically react to release hydrogen, which can diffuse into the surface of non-coated fasteners. Steels with high-carbon contents, heat treated to high strengths, are most susceptible to stress embrittlement.
All hydrogen embrittlement failures are intergranular – but not all intergranular failures can be attributed to hydrogen embrittlement.
Note these examples:
- Three self-drilling screws fastened a curved plastic sill plate to a car door liner. The middle screw frequently failed in factory assembly. Analysis showed misalignment where the sill met the curved metal frame under the middle screw. Also, a factory wash test allowed moisture to hit the misaligned screw, acting as an electrolyte in a galvanic corrosion cell that then generated hydrogen. The hydrogen gas migrated to the over-stressed (due to bending) middle screw, causing a hydrogen-assisted stress corrosion failure.
- Case hardened fasteners used to hold structural aluminum members to steel beams in a U-channel configuration is another example. These channels, used to retain glass windows, had drainage holes in their tracks. The fasteners were coated with a zinc-bearing, corrosion-resistant, organic compound. Environmental moisture from the glass collected in the tracks, causing a galvanic reaction, which generated hydrogen and subsequent fastener failure.
- Structural aluminum stadium bleacher seats bolted to concrete. During rain, calcium from the concrete became the corrosion agent.
- Screws holding turn signal lights on auto right rear quarter panels were failing in the factory prior to car shipment. The cause for this failure could be found in the fact that assembled cars were tested for water leaks with high pressure jets from an enclosed circulating system. Bacteria/sludge problems in the wash were controlled by adding two gallons of sodium hypochlorite daily. But, concentration levels weren’t monitored. After 3 months, the concentration built to a level high enough to cause stress corrosion cracking of the fasteners. Car design was such that the pressurized wash could not penetrate signal light joints on the left car side, hence only failures on the right. Interestingly, the fasteners were mechanically galvanized to guard against hydrogen pickup during manufacture. However, the galvanization could not guard the joint from environmental hydrogen pickup.
14. WHAT ARE THE MARKS SHOWN ON THE HEAD OF A BOLT?
Usually fastener standards specify two types of marks to be on the head of a bolt. The manufacturer’s mark is a symbol identifying the manufacturer (or importer). This is the organization that accepts the responsibility that the fastener meets specified requirements. The grade mark is a standardized mark that identifies the material properties that the fastener meets. For example, L7B7 on a bolt head indicates that the grade of bolt and ATP is the manufacturer’s mark.
Both marks are usually located on the top of the bolt head, most standards indicating that the marks can be raised or depressed. Raised marks are usually preferred by manufacturers because these can only be added during the forging process whereas depressed marks can be subsequently added (possibly with illegitimate marks).
15. HOW DO I ORDER BOLTS?
What information do I need to provide when ordering bolts or requesting a quotation to ensure that I receive the correct product? Below is list of information to provide and an explanation of how each factor effects price and lead time.
The speed with which you require your quotation back has no effect on the price or delivery of your order. However, if you let us know how quickly you need your pricing, we will be better able to accommodate your needs. In addition, based on this information, we will also be able to better prioritize the rest of our workload.
All-Pro Fastener’s lead times are based on our customers’ requirements. However, we have standard lead times that are the basis of our scheduling when customers are not pressed for delivery. Should materials be needed quicker than our standard lead times, we are able to expedite the manufacturing process, however additional costs to cover overtime labor may be incurred. Therefore, lead times could affect the price.
It is important to clearly communicate any domestic requirements. In almost all cases, domestic product is more expensive than the identical imported item. Many of the smaller standard fasteners that All-Pro Fasteners stocks are imported. However, these same fasteners can be sourced domestically or manufactured within our facility. Virtually all of the steel round bar All-Pro uses to manufacture bolts is domestic, as are the standard washers we stock. Nuts are dual inventoried both import and domestic.
For custom manufactured items, the size of a run has a significant impact on the unit cost of a part. There are fixed costs associated with the production of any fastener and can include equipment set up costs and testing charges. These costs are the same regardless of the size of the production run. When broken down into a per-part cost, they are reduced as the quantity increases. Quantity can also have an effect on the lead time required to produce a run of product. Extremely large runs may require more machine hours and therefore may take additional time to manufacture.
The diameter and length of a fastener have a dramatic effect on the cost of a bolt. Since the steel used to manufacture bolts is bought and sold on a per pound basis, the heavier the bolt, the more expensive it will be.
Construction fasteners can be produced and supplied with a corrosion resistant coating or in bare metal (referred to as plain finish or black). The most common corrosion resistant coating is hot-dip galvanized, however zinc plated and other options are available as well. The different coatings will not only add to the cost of a plain finish fastener, but it will also lengthen the lead time.
The grade of a bolt, whether ASTM, SAE, or AASHTO, has an impact on the cost. Since various grades of bolts use different types of raw material, costs vary depending on the chemical composition of the steel round bar used. Additionally, some specifications require heat treating or special testing, both of which add to the cost and lead time to produce the fastener.
The type of a bolt (e.g., headed bolt, bent bolt, or straight rod) will have an effect on the cost and lead time. Certain fastener types require more or fewer manufacturing operations than others. The time to process each operation will affect the price. Since different pieces of equipment and machinery are used depending on the configuration, lead times will vary according to the type of fastener required.
Contrary to popular belief, there is no such thing as a “standard thread length” for the vast majority of construction fasteners. ASME outlines some standards for headed bolts, but often more thread is required. It is important to clearly communicate desired thread lengths on headed bolts in addition to bent bolts and threaded rods.
Nuts, Washers, and Accessories
If nuts, washers, anchor sleeves, anchor plates, and other accessories are required with your bolts, it will definitely affect the unit cost. Special nuts, washers, and accessories might also take longer to produce than the bolt itself.
All-Pro Fastener’s account managers are trained to provide the least expensive compatible nut and washer for the grade of bolt being provided. If a different grade of nut or washer is required it is important to communicate that information.
Certification and Special Testing
Unless otherwise specified, All-Pro Fasteners will provide chemical and physical mill test reports for all domestic, high strength, and custom manufactured bolts and accessories. Testing of fasteners, many of which are performed within our own in-house testing laboratory, will be in accordance with the ASTM, AASHTO, or SAE specification, according to the bolt order. Any additional testing or special certification can be provided upon request.
With regard to quotes, let us know if you would like your bolt prices to include the cost of shipping the product. We can either quote your list of products delivered to its destination or we can exclude the freight costs from our estimate. On orders, we can ship with freight prepaid, third party, or collect, on a carrier of your choice.
16. WHAT IS THE DIFFERENCE BETWEEN A BOLT MANUFACTURER AND A FASTENER DISTRIBUTOR? WHAT IS ALL-PRO FASTENERS?
In the fastener industry, there are normally two different types of companies – distributors and manufacturers.
Distributors buy and resell product that is readily available in the marketplace. These items are typically smaller sized fasteners that are mass produced either overseas, or in some cases, the United States. Distributors provide both SAE fasteners (grades 2, 5 and 8) for use in equipment, automotive, and OEM type applications as well as ASTM fasteners, more commonly used in construction. For a distributor to stock a specific fastener, they must sell it on a repetitive basis frequently enough to justify inventorying that item. Products that are commonly stocked by distributors include A325 structural bolts, small diameter A307 hex bolts, wood screws, rivets, wedge anchors, all thread rod, nuts, washers, etc. These items are ordered frequently, so a distributor is normally able to carry a complete size range of these items.
Unlike fastener distributors, bolt manufacturers like All-Pro Fasteners specialize in producing fasteners that are not readily available in the marketplace. These are bolts that are specifically engineered into a structure and do not meet the dimensional, chemical, and mechanical properties that would commonly be found sitting on the shelf of a fastener distributor. Typically, nonstandard fasteners are large in diameter, longer in length, or higher in strength than common, mass produced fasteners. At All-Pro we are manufacturing bolts that are not in stock. We have specialized equipment designed to take steel round bar and cut it, thread it, forge a head onto it, bend it, or otherwise process it and turn it into a finished fastener.
All-Pro Fasteners is considered a hybrid, both distributor and manufacturer.
The distinction between bolt manufacturers and fastener distributors is not cut and dried and is often blurred by hybrid fastener companies. All-Pro Fasteners has an extensive complement of manufacturing capabilities, but also stocks and distributes a complete line of standard fasteners and industrial supplies.
At All-Pro we take it step further and have built an in-house Quality Lab that is A2LA accredited and ISO Certified. Having this lab sets All-Pro apart from a majority of other manufacturers and distributors, because all of our distributed and manufactured product is tested by the lab before being shipped to the customer.
17. WHAT IS API AND WHY IS IT IMPORTANT?
The American Petroleum Institute (API) is the only national trade association representing all facets of the oil and natural gas industry, supporting 10.3 million U.S. jobs and nearly 8 percent of the U.S. economy. API’s more than 625 members include large integrated energy companies, as well as exploration and production, refining, marketing, pipeline, and marine businesses, along with service and supply firms. These companies provide most of the nation’s energy and are backed by a growing grassroots movement of more than 40 million Americans.
Although this organization’s focus is primarily domestic, in recent years its work has expanded to include a growing international dimension. Today API is recognized around the world for its broad range of programs:
API’s mission is to promote safety across the industry globally and to influence public policy in support of a strong, viable U.S. oil and natural gas industry.
Research & Statistics
API conducts or sponsors research ranging from economic analyses to toxicological testing. The association collects, maintains, and publishes statistics and data on all aspects of U.S. industry operations, including supply and demand for various products, imports and exports, drilling activities and costs, and well completions. This data provides timely indicators of industry trends. API’s Weekly Statistical Bulletin is one of the most recognized publications, widely reported by the media.
For more than 90 years, API has led the development of petroleum, natural gas and petrochemical equipment, along with related operating standards. These standards represent the industry’s collective wisdom on everything from drill bits to environmental protection, and embrace proven, sound engineering and operating practices, along with safe, interchangeable equipment and materials. API maintains nearly 700 standards and recommended practices. Many have been incorporated into state and federal regulations. These standards and recommended practices are also the most widely cited standards by the international regulatory community.
All-Pro Fasteners’ on-site manufacturing, All-Pro Threaded Products™ is ISO 9001, API Q1. This facility also holds the America Petroleum Institute API 20F-002 and API 20E-0016 Monogram Licenses to manufacture API 20E BSL-1, BSL-2, BSL-3 bolting. Having these certifications provides our customers confidence in their critical-application and safety-related fasteners. That confidence, along with our ability to turn critical quality parts in a timely manner, means they can count on us for all specially manufactured parts, forged or machined.
18. WHAT ARE THE ADVANTAGES OF BUYING DIRECTLY FROM A MANUFACTURER LIKE ALL-PRO FASTENERS?
Expertise regarding nonstandard product
All-Pro Fasteners serves multiple vertical markets in the fastener world. We make non-standard fasteners and a broad range of fastener-related items. Therefore, we need to be experts in all related areas. Our account managers are extremely knowledgeable with regard to the ASTM specifications, covering all types of fasteners as well as their application.
Direct line of communication… we make it easy
At All-Pro Fasteners, our account managers walk you through the process of ordering the product. We ask all of the pertinent questions necessary to ensure you receive the proper bolts as specified. If you don’t know exactly what you need, we will assist you in the process of locating that information.
Our team is trained to make sure you get the right grade, finish, configuration, dimensions, compatible nuts and washers, and ensure they are delivered on your schedule. We take the difficulty and uncertainty out of buying product. We ask a lot of questions, because we feel it is our obligation to ensure that you order these items correctly. The next time you need nonstandard/standard product, let us show you how easy we can make the process.
The employees at All-Pro Fasteners make our customers’ problems our problems. By working with our customers to overcome their obstacles, we create a true partnership.