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6.2. Ordering Bolts
The manufacturing quality requirements for high-strength bolts, nuts, and washers are covered in the following specifications: for high-strength bolts and for tension control bolt/nut/washer assemblies, ASTM F3125/F3125M; for nuts, ASTM A563/A563M or ASTM A194/ A194M; and for washers, ASTM F436/F436M. These fasteners should be specified and accepted based upon the criteria established therein.
ASTM standard specifications for fasteners used in U.S. construction follow a format that include ordering information in one section. As an example, the following is taken from ASTM F3125 Section 3:
3.1 Orders for bolts under this specification shall include:
3.1.1 ASTM designation.
Number of bolts or assemblies, including washers, if required.
Including nominal bolt diameter and bolt length, and thread pitch if other than standard.
A325, A490, F1852, F2280 or A325M, A490M.
Type 1 or Type 3. When Type is not specified either Type 1 or Type 3 may be furnished at the supplier’s option.
Heavy Hex or Twist-Off Style.
3.1.7 Coatings or finishes:
If other than plain finish, specify the coating process or finish required, see Annex A1
The section goes on to list information that may be required for some fasteners, such as rotational capacity testing or shipment as an assembly with a washer and nut. For structural fasteners, you must order test reports.
As indicated in the RCSC Specification Commentary, there are four cases in which bolts and nuts must be treated as a manufactured matched assembly:
- when bolts are galvanized (Commentary Section 2.8)
- when “tension-control” bolts are specified (Commentary Sections 2.4.1 and ASTM F3125 Section 16.1.5)
- when ASTM F3148 spline drive bolts are installed using the combined method (RCSC Section 2.4.2)
- when rotational capacity testing is required.
For galvanized bolts, because nut-thread over-tapping to accommodate the added thickness of galvanizing may reduce the nut stripping strength, ASTM F3125 requires that galvanized nuts be lubricated and tested by the responsible party (manufacturer or distributor) to ensure adequate rotational capacity. For "tension-control" bolts, only mechanical galvanizing is permitted because it provides a thinner more uniform coating
6.2.4. Is it acceptable to substitute ASTM A354 Grade BC, ASTM A354 Grade BD, or ASTM A449 bolts for ASTM F3125 Grades A325 or A490 bolts?
In general, it is not acceptable to substitute ASTM A354 Grade BC, ASTM A354 Grade BD, or ASTM A449 bolts for ASTM F3125 Grades A325 or A490 bolts. ASTM F3125 bolts are made to dimensions provided by ASME B .18.2.6. Both F3125 and B18.2.6 have maximum diameters of 1½ in. and a maximum length of 12 diameters. ASTM A354 and ASTM A449 are more general standards, not restricted to structural bolts. They also apply to studs and other externally threaded fasteners. Therefore, they do not have the provisions included in the structural bolt standards. The dimensions, particularly thread length, are not the same. ASTM A354 bolts are hex, not heavy hex, unless the purchaser specifies heavy hex. ASTM A449 has no default for bolts so the purchaser has to define what dimensions are required. The Turn of Nut pretensioning method specifies the number of turns beyond an initial tightness to result in the required pretension. The number of turns depends on the thread length, or the resulting unthreaded length. A standard number of turns has not been published for bolts that do not confirm with B18.2.6. Therefore, the pretensioning procedure for ASTM A354 and ASTM A449 bolts has to be developed and tested by the user.
6.2.5. Is it acceptable to substitute SAE J429 grades 5 and 8 bolts for ASTM F3125 Grades A325 and A490 bolts, respectively?
No, it is not acceptable to substitute SAE J429 Grades 5 and 8 bolts for ASTM F3125 Grades A325 and A490 bolts, respectively. The strength properties of SAE J429 Grade 5 bolts and Grade A325 bolts are identical; likewise, SAE J429 Grade 8 bolts are the strength equivalent of Grade A490 bolts. However, these material specifications differ in that Grades A325 and A490 specify thread length and head size, whereas SAE J429 does not. Additionally, quality assurance and inspection requirements for Grades A325 and A490 bolts are more stringent.
The “T” in the designation ASTM F3125 Grade A325T invokes supplement S1 in ASTM F3125, which allows for full-length threading. This provision may be specified for Grade A325 bolts of length less than or equal to four times the bolt diameter only; there is no similar provision for Grade A490. The fully threaded bolt allows the fabricator or erector the option to use a single-length fastener in the majority of bolting applications if desired. Note that if Grade A325T bolts are specified, it is impossible to exclude the threads from the shear plane and the design must be based upon the “threads included” strength values. Fully threaded Grade A325 bolts are marked on the head of the bolt with “A325T” instead of “A325” so that they can be identified even after installation.
Note that bolts marked A325S or A490S have a dimension that varies from the standard so installation turns and assumptions about the faying surface relative to the shank length have to be checked.