ASTM A586 is the spec for galvanized structural strand, an arrangement of wires laid helically around a center wire to produce a symmetrical cross section, used as a load-carrying tension member where great flexibility and bending are not major requirements [S1].
ASTM A603 governs the heavier cousin, zinc-coated structural wire rope built from six strands laid helically around a core (another strand or a smaller wire rope), and is the structural cable of choice where bending ability is required, such as forming flemish eye ends and drop terminals [S1]. At Bethlehem/Wirerope Works, A586 strand is produced up to 5-1/2 inch diameter, while A603 rope extends to 7 inch diameter [S1].
Construction and mechanical character
A586 strand is the least flexible of steel cables for any given diameter because every wire runs straight along the axis in one helical layer set; the payoff is a high strength-to-weight ratio, a high modulus of elasticity, and a small diameter-per-unit strength [S1]. Lexco Cable catalogs A586 galvanized structural strand in 1/2 inch to 1 inch diameter with constructions such as 1x19, the standard coarse strand used in bridge stay and suspender service [S2][S5].
A603 rope trades some of that axial stiffness for genuine bending life: six independent strands over a core let the rope spool, terminate in a socket, and absorb curvature at end fittings without permanently kinking the outer wires [S1]. National Strand's A586 bridge strand data sheet lists 19-wire strand, 11/16 inch to 1 inch standard diameter, coated-wire diameter 0.137 inch to 0.200 inch, and Class A breaking strength from 58,000 lb to 122,000 lb across that diameter band, with strand mass 999 lb to 2,073 lb per 1,000 ft [S3].
Zinc coating classes and grade selection
A586 splits into Grade 1 (EHS, extra-high strength) and Grade 2 (HS, high strength), and then layers four coating classes A through C over those grades, with Class A being the thickest zinc mass per unit area on every wire in the strand [S2]. Texas DOT Special Specification 4181 for cable hangers calls out pre-stretched galvanized spiral strand conforming to ASTM A586, Grade 2, with a Class A coating throughout, the conservative pick for hanger service where corrosion and fatigue both matter [S6].
Lexco's catalog table exposes the four practical coating permutations available off the shelf: Class A throughout, Class A inner with Class B outer, Class A inner with Class C outer, and Class A throughout at Grade 2; the mixed Class-B-outer and Class-C-outer options exist to cut cost on the visible wires while keeping the corrosion-critical inner wires heavily galvanized [S2]. The Wire Rope 101 engineering reference summarizes the trade bluntly: A586 galvanized structural strand is less flexible than structural rope, but stronger with a higher modulus, which is exactly why it survives as a primary stay or suspender while rope is reserved for curved load paths [S7].
High-strength variants and the 15% breaking-force upgrade
SS-265 is a proprietary high-strength structural strand from Wire Rope Works designed specifically for tower guying; it delivers a 15% increase in minimum breaking force over standard strand manufactured to ASTM A586, and at the same nominal 2 inch diameter the minimum breaking force rises from 245 tons to 282 tons [S1][S4]. The same 15% gain lets a designer either downsize the strand diameter (smaller fittings, less weight per linear foot, lower cost per foot) or stay at the original diameter and pick up a higher design factor on the guy system [S1][S4].
At National Strand, A586 Grade 1 or 2 high-strength bridge strand is positioned against equal-diameter EHS Grade strand as delivering smaller yet stronger options in some instances, a direct parallel to the SS-265 argument, with the additional benefit that the same A586 designation keeps the specifier inside the standard bridge strand universe rather than a proprietary SKU [S3]. For routine pedestrian bridge, suspender, and stay-cable service the A586 + Grade 2 + Class A combination remains the workhorse spec; SS-265 enters the bill of material when tower guying forces, headroom, or weight budgets push the standard table off the end [S1][S3][S4][S6].
Comparison matrix: A586 strand vs A603 rope
Decision criteria, with sources: (1) Construction: A586 is a single layer of helical wires around a center wire, e.g. 1x19; A603 is 6 strands laid over a core [S1][S2]. (2) Maximum manufactured diameter: A586 to 5-1/2 inch, A603 to 7 inch at Wire Rope Works [S1]. (3) Flexibility: A586 is the least flexible steel cable for its diameter; A603 is built specifically for bending and flemish-eye termination [S1]. (4) Modulus and strength efficiency: A586 wins on modulus and diameter-per-unit-strength; A603 wins where end-termination efficiency and fatigue under bending dominate [S1][S7]. (5) Coating options: A586 ships in Grade 1 or 2 and four Class A/B/C permutations; A603 is governed by the same zinc-coated wire regime but the spec is written around rope mechanics, not strand layers [S2][S6]. (6) Typical breaking strength: A586 Class A from 58,000 lb (11/16 inch) to 122,000 lb (1 inch) at National Strand, with the 2 inch SS-265 variant reaching 282 tons (564,000 lb) [S3][S1].
Use the matrix in spec meetings: write A586 into the drawings for primary tension members with static or quasi-static loads, guys, and main/suspender/stay cables on bridges; write A603 into the drawings for catenary curves, flemish-eye assemblies, and any cable that has to bend over a saddle or wrap a socket under load [S1][S3][S6][S7]. Related steel-cable selection logic, including the structural strand family and the broader prestressing strand comparison, is covered in the encyclopedia, with the upstream wire rod feed controlling the chemistry that both specs depend on.
Safety factors and common misuse
Wire rope and aircraft cable should never be used at breaking strength; Lexco's A586 catalog warning sets a 10:1 safety factor minimum for critical or overhead applications, and a 5:1 factor should be divided into the assembly's actual strength because end fittings do not always hold 100% of the rope's strength efficiency, with a pull test recommended for quality assurance [S2]. That warning is spec-agnostic, but it lands hardest on A603 rope because rope assemblies are the ones that get terminated, socketed, and field-spliced; A586 strand assemblies in bridge and tower service tend to use the heavier end-termination hardware that approaches the parent strand's strength, but the same 5:1 rule still applies to the assembly-level rating [S2][S6].
A second common misuse is treating the two specs as interchangeable: specifying A603 for a primary bridge stay wastes flexibility, adds stretch, and increases diameter for the same breaking strength; specifying A586 for a catenary that has to flex over a tower saddle invites fatigue cracking of the outer wires and eventual strand failure at the bend [S1][S7]. When in doubt, follow the structure: stationary straight tension member equals A586; tension member with a controlled bend, flemish eye, or socket termination equals A603 [S1].
Sourcing, certification, and what to ask the mill
Wire Rope Works holds API certification, recognition from ABS, DNV, and Lloyd's of London, plus ISO 9001:2000, and ships Statistical Process Control data covering wire manufacture, rope/strand manufacture to order specification, tensile strength, modulus of elasticity, actual breaking force, prestretching, measuring, and proof loading, with material certification available from end-termination vendors [S1]. National Strand publishes cut sheets, brochures, a shipment calculator, and color-coded end-cap charts for its A586 bridge strand range, which simplifies receiving inspection on a bridge job [S3].
For procurement, the minimum data the mill should return with shipment: ASTM designation and revision year (A586 or A603), grade (1 or 2 for A586), coating class (A, B, or C on inner and outer wires), nominal diameter, measured breaking strength in tons or kN, modulus, unit mass per foot or metre, prestretch certificate if specified, and coating mass per unit area on inner and outer wires separately [S1][S2][S6]. The cable wire encyclopedia entry covers the upstream zinc-coated wire grades that feed both A586 and A603, and the draw-wire sensor reference is the right starting point if the structural strand is being instrumented for live load monitoring on a new tied-arch or cable-stayed bridge. For news context on the ASTM A1035 Grade 100 vs Grade 120 rebar selection logic that often runs in the same bridge contract documents, see that walkthrough.
Trackable signal: confirm the 2026 revision status of ASTM A586 and A603 against your project specification year before issuing the mill order, because zinc-coating class tables and Grade 1/Grade 2 minimum breaking strength values have been tightened in past revisions and the project's reference year controls which line of the table is binding [S1][S2].