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, ASTM A325/A325M and ASTM A490/A490M; for nuts, ASTM A563/A563M or ASTM A194/ A194M; for washers, ASTM F436/F436M; for direct tension indicators, ASTM F959/F959M; and for tension control bolt/ nut/washer assemblies, ASTM F1852 and ASTM 2280. These fasteners should be specified and accepted based upon the criteria established therein.
From RCSC Educational Bulletin No. 3 (see www. boltcouncil.org), the purchase order for high-strength bolts must include the ASTM grade (A325 or A490), the type (1 or 3), a copy of the project specification for the manufacturer or vendor, and the “Ordering Information” as required by the appropriate ASTM Specification. Additionally, the purchase order should require the following:
1. That the vendor provide certification that the bolts, nuts, and washers furnished conform to all requirements of the referenced ASTM specification.
2. That certified manufacturer’s mill test reports be supplied that clearly show the applicable ASTM mechanical and chemical requirements together with the actual test results for the lot of supplied fasteners.
3. That the bolt heads and the nuts of the supplied fasteners be marked with the manufacturer’s identification mark and the ASTM grade and type as specified in ASTM specifications.
4. For projects requiring slip-critical connections, that the lubricated bolt, nut and washer be pre-assembled to ensure proper fit of the bolt and nut and that the lot be tested for strength prior to shipment to the purchaser to meet the requirements of the 2004 RCSC Specification Table 4.
As indicated in the RCSC Specification Commentary, there are two cases in which bolts and nuts must be treated as a manufactured matched assembly: when bolts are galvanized (Commentary Section 2.3.3) and when “tension-control” bolts are specified (Commentary Sections 2.2 and 8.2.3). In the former case, because nut-thread over-tapping to accommodate the added thickness of galvanizing may reduce the nut stripping strength, ASTM A325 requires that the galvanized assembly be lubricated and tested by the manufacturer to ensure adequate rotational capacity. In the latter case, some of the negative aspects of this torque-controlled installation method are minimized through good quality control in the matched assembly.
6.2.4. Is it acceptable to substitute ASTM Grade BC, A354 Grade BD or A449 bolts for ASTM A325 or A490 bolts?
In general, this is not an acceptable substitution. While ASTM A449 seems to offer the same strength as ASTM A325, the use of A449 material is restricted in the Specification Section J3.1 to bolt diameters larger than 1½ in. or lengths exceeding 12 diameters. This is because these bolts are not produced to the same inspection and quality assurance requirements as ASTM A325 bolts. If the bolts must be pre-tensioned, the bolt geometry including the thread pitch, thread length, head and nut(s) shall be equal to or (if larger in diameter) proportional to that required by the RCSC Specification. Installation shall comply with all applicable requirements of the RCSC Specification with modifications as required for the increased diameter and/or length to provide the design pretension.
6.2.5. Is it acceptable to substitute SAE J429 grades 5 and 8 bolts for ASTM A325 and A490 bolts, respectively?
No. The strength properties of SAE J429 grade 5 bolts and ASTM A325 bolts are identical; likewise, SAE J429 grade 8 bolts are the strength equivalent of ASTM A490 bolts. These material specifications differ, however, in that ASTM A325 and A490 specify thread length and head size, whereas SAE J429 does not. Additionally, quality assurance and inspection requirements for ASTM A325 and A490 bolts are more stringent.
The “T” in the designation ASTM A325T invokes supplement S1 in ASTM A325, which allows for full-length threading (ASTM A325T). This provision may be specified for ASTM A325 bolts of length less than or equal to four times the bolt diameter only; there is no similar provision in ASTM A490. The fully threaded bolt allows the fabricator the option to use a single-length fastener in the majority of bolting applications, if desired. Note that if ASTM 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 A325 bolts are marked on the head of the bolt with “A325T” instead of “A325”, so that they can be identified even after installation.