ASME B18.31.3 specifies the dimensions and tolerances for inch left-hand fully threaded rod. The full dimensional table is reproduced below, followed by the DIN, ISO and ASME parts that match or supersede it.
- Standard
- ASME B18.31.3
- Product
- Inch Left-Hand Fully Threaded Rod
- Governing standards
- ASME B18.31.3 and ASME B1.1 LH
Equivalence between national standards is dimensional, not always metallurgical. Check the property class separately when substituting.
Inch Left-Hand Fully Threaded Rod manufactured to ASME B18.31.3 are dimensioned by the size table reproduced on this page. The standard fixes geometry and tolerances only; material and property class are assigned by ISO 898-1/898-2, and surface finish by separate finish standards.
ASME B18.31.3 — Scope
ASME B18.31.3 specifies the dimensions and tolerances of inch left-hand fully threaded rod. Material, property class, surface finish and packaging are governed by separate documents in the same standards family (for example ISO 898-1 for the mechanical property classes of bolts and screws).
Tolerance & Product Grades
ASME B18.31.3, alongside the related ASME B18.31.3 and ASME B1.1 LH entries on this site, specifies product grades (typically A or B for fine work and C for general engineering) and tolerance classes for the controlling dimensions. Choose the grade against the precision your application requires.
Dimensions Specified by ASME B18.31.3
| Nominal size | Thread hand | Thread class | Standard lengths (in/ft) | Material options | Reference standard |
|---|
| 6-32 | left-hand | 2A | 12 / 24 in and 3 ft | zinc-plated steel / 18-8 stainless / 316 stainless | ASME B18.31.3 and ASME B1.1 LH |
| 8-32 | left-hand | 2A | 12 / 24 in and 3 ft | zinc-plated steel / 18-8 stainless / 316 stainless | ASME B18.31.3 and ASME B1.1 LH |
| 10-24 | left-hand | 2A | 12 / 24 in and 3 ft | zinc-plated steel / 18-8 stainless / 316 stainless | ASME B18.31.3 and ASME B1.1 LH |
| 1/4-20 | left-hand | 2A | 12 / 24 in and 3 ft | zinc-plated steel / 18-8 stainless / 316 stainless | ASME B18.31.3 and ASME B1.1 LH |
| 3/8-16 | left-hand | 2A | 12 / 24 in and 3 ft | zinc-plated steel / 18-8 stainless / 316 stainless | ASME B18.31.3 and ASME B1.1 LH |
| 1/2-13 | left-hand | 2A | 12 / 24 in and 3 ft | zinc-plated steel / 18-8 stainless / 316 stainless | ASME B18.31.3 and ASME B1.1 LH |
Companion Standards
ASME B18.31.3 controls only the geometry of inch left-hand fully threaded rod. The mechanical strength is set by ISO 898-1 (bolts and screws) or ISO 898-2 (nuts); the surface finish is governed by separate finish standards (e.g. ISO 4042 for electroplating). For corrosion testing, the relevant document is ISO 9227 (neutral salt spray).
When to Specify ASME B18.31.3
ASME B18.31.3 is the inch-based reference; for metric programs choose the ISO equivalent instead.
Applications & Industries
Where Inch Left-Hand Fully Threaded Rod are used, and what decides the specification in each case. Stocked from 6-32 to 1/2-13 (screw size).
Industries that specify Inch Left-Hand Fully Threaded Rod
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Opposed adjusters
Left-hand and right-hand rod pairs used to change length without disconnecting the joint.
-
Rotating equipment
Threaded adjustments arranged to resist self-loosening in service.
-
Machine fixtures
Inch adjustment rods where the thread hand is part of the mechanism.
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Repair and fabrication
Replacement rod matched to existing left-hand nuts and couplers.
-
Pressure equipment & flanges
Studs and nuts on flanged joints, where both ends are tightened and the assembly is inspected.
-
Plant & machine installation
Anchoring and levelling machines onto bases and frames.
Typical applications
- providing a left-hand threaded member for an opposed adjuster
- matching the rod to a left-hand nut rather than a standard right-hand nut
- holding a threaded adjustment against rotation in a paired mechanism
- specifying inch thread class, hand, length and material together
- clamping a joint from both ends where a headed bolt will not fit
- suspending services from a soffit on threaded rod
Service conditions to specify against
- Marine and coastal
- Available in A4 (316) stainless for chloride exposure — coastal structures, pool halls, water treatment and deck hardware, where A2 will eventually pit.
- High load
- Supplied in ISO 898-1 property classes, so the joint can be designed to a stated proof load and tightened to a calculated torque rather than by feel.
Where to use something else
- Do not pair a left-hand rod with an ordinary right-hand nut; the threads will not engage correctly.
- Not for a joint that must be tightened from one side only — there is no head to hold.
Full application guide: where Inch Left-Hand Fully Threaded Rod are used, how to specify them, and the cases they are wrong for
