ASME B18.31.2 Continuous Thread Studs — UNC Threads, 1/4 – 4 in
ASME B18.31.2 continuous thread stud dimensions — thread size, TPI, and the source's per-size table from 1/4 through 4 in UNC, with the designation convention and length-increment rules the source prints, transcribed row-for-row.
Last updated: 2026-11
Specifications
A continuous thread stud is a bar threaded over its full usable length — no wrench-flat, no head, no unthreaded grip — designed to thread into a tapped hole at one end and carry a nut (or two, or a nut plus turnaround) at the other. It is the hardware of flanged joints, engine heads, pressure equipment and anywhere the stud is screwed into a body once and the load-bearing end assembled and disassembled repeatedly: the tapped-hole thread (the more expensive one to re-cut) stays virgin while wear lands on the replaceable nut end. ASME B18.31.2 is the governing inch standard, and the collected chart tabulates 1/4 through 4 in with thread designation and TPI per row (13 rows; note the flagged quirk carried below — the source prints "..." in the 8-UN column at the 1/4 – 1 in sizes, reproduced as printed). The designation convention is the practical ordering language: studs are specified by diameter, thread series and length — and per the source's example, thread ends are chamfered and the length increments follow the source's rule (note that close-length practices differ by purchaser spec). Grade, material, coating and machined-from-bar vs rolled-thread process are not tabulated by the collected chart — per RFQ; B7/B16 pressure-vessel grades pair with ASTM/ASME material specs on the drawing.
| Standard | ASME B18.31.2 — continuous thread studs, inch series (threaded over full usable length; no head, no wrench flats) |
|---|---|
| Size range | 1/4 – 4 in, 13 printed rows; UNC coarse TPI ladder (20 down to 4) with 8-UN constant-pitch column as printed (see table footnote at 1/4 – 1 in) |
| Designation | Diameter x thread x length (source's designation example printed on the chart); chamfered thread ends per source |
| Length increments | Length-increment rule as printed by the source note — state exact length and increment practice at RFQ |
| Grade / material / coating | Not tabulated by the collected chart — per RFQ (pressure-vessel service typically B7/B16 grades to the material spec on the drawing; rolled vs cut thread is a process RFQ line) |
| D (fractional) | D (decimal) | UNC TPI | UNF TPI | 8UN TPI | UNC Runout (min) | UNC Runout (max) | UNF Runout (min) | UNF Runout (max) | 8UN Runout (min) | 8UN Runout (max) |
|---|---|---|---|---|---|---|---|---|---|---|
| 1/4 | 0.2500 | 20 | 28 | - | 0.050 | 0.100 | 0.036 | 0.071 | - | - |
| 5/16 | 0.3125 | 18 | 24 | - | 0.056 | 0.111 | 0.042 | 0.083 | - | - |
| 3/8 | 0.3750 | 16 | 24 | - | 0.063 | 0.125 | 0.042 | 0.083 | - | - |
| 7/16 | 0.4375 | 14 | 20 | - | 0.072 | 0.143 | 0.050 | 0.100 | - | - |
| 1/2 | 0.5000 | 13 | 20 | - | 0.077 | 0.154 | 0.050 | 0.100 | - | - |
| 5/8 | 0.6250 | 11 | 18 | - | 0.091 | 0.182 | 0.056 | 0.111 | - | - |
| 3/4 | 0.7500 | 10 | 16 | - | 0.100 | 0.200 | 0.063 | 0.125 | - | - |
| 7/8 | 0.8750 | 9 | 14 | - | 0.111 | 0.222 | 0.072 | 0.143 | - | - |
| 1 | 1.0000 | 8 | 12 | - | 0.125 | 0.250 | 0.084 | 0.167 | - | - |
| 1 1/8 | 1.1250 | 7 | 12 | 8 | 0.143 | 0.286 | 0.084 | 0.167 | 0.125 | 0.250 |
| 1 1/4 | 1.2500 | 7 | 12 | 8 | 0.143 | 0.286 | 0.084 | 0.167 | 0.125 | 0.250 |
| 1 3/8 | 1.3750 | 6 | 12 | 8 | 0.167 | 0.333 | 0.084 | 0.167 | 0.125 | 0.250 |
| 1 1/2 | 1.5000 | 6 | 12 | 8 | 0.167 | 0.333 | 0.084 | 0.167 | 0.125 | 0.250 |
- Row 1 (1/4): The source prints "..." in the 8UN TPI and 8UN runout columns for 1/4–1 in — the 8UN series simply is not offered at those diameters; shown here as "—".
Materials
- Stud grade and material are drawing-level decisions (B7/B16 for pressure equipment, machine grades elsewhere); coating sequence interacts with tapped-hole fit — specify at RFQ
Ordering & documentation
Documents
Shipments are backed by Mill Test Certificate (MTC), Dimensional Report, Salt Spray Test Report on request, with full batch traceability from raw material to finished product. Quality management follows the owner-confirmed compliance list: ISO 9001:2015, RoHS, REACH. Exact document sets are confirmed on the order.
Quotation
- The fastener family (ASME B18.31.2 Continuous Thread Studs — UNC Threads, 1/4 – 4 in) plus the standard designation from your drawing — DIN / ISO / JIS / ASTM / ANSI, or a drawing for custom parts.
- Size (diameter and length), thread type (metric or inch), property class or grade, and coating or finish.
- Quantity per size and your target delivery date.
- Destination country, and any required documents (for example a mill test certificate) so the quote includes them.
Sample & supply
Minimum order quantity is 1,000–10,000 pieces depending on size. Stock items run 3–7 days. High-strength and custom parts run 15–25 days. Quantities or variants outside the standard range are confirmed at quotation.
Storage & shipping
Parts are packed for export and shipped factory-direct to buyers in Europe, Asia, the Americas and the Middle East. Store fasteners dry and protected until installation, and keep coated parts in their packaging until use; specific packing and preservation requirements can be stated on the order and confirmed at quotation.
Frequently asked questions
Why choose a continuous thread stud over a bolt for a flanged or tapped-hole joint — and what must be specified beyond the chart?
The stud wins where the joint lives and dies by the nut end. Screwed into a tapped body once, the stud puts the repeated assembly cycle on the nut side: studs are cheap to replace and re-torque, the body's tapped thread — the part that ruins castings and machined bodies when it strips — never wears, and both ends can be torqued simultaneously for even gasket compression on flanges, which a headed bolt cannot do from one side. Continuous (full) thread maximizes engagement flexibility: the stud seats to any depth the hole offers, and the nut travels anywhere along the length — the reason it is the default for long through-flange stacks and insulation extensions. What the chart cannot order for you is the specification half: the collected table covers thread designation and TPI only, so grade/material (B7/B16 for pressure-vessel service with their own ASTM specs, machine grades elsewhere), thread class (2A as commercial, heavier classes per RFQ), coating (plating or galvanizing changes the fit into the tapped hole — see the internal 6H/2B allowance discussion), and rolled-vs-cut thread (rolled is stronger in fatigue, cut gives tighter runout) all arrive as RFQ lines. State stud diameter-series-length plus grade and finish together, and name the tapped-hole engagement depth on the drawing — a stud with too little engagement in a soft body is a pulled thread waiting to happen.
What is the MOQ and lead time for studs on this standard?
The minimum order quantity is 1,000–10,000 pieces depending on size. Stock items ship in 3–7 days; high-strength and custom parts in 15–25 days. Common stud sizes are widely stocked; confirm the exact schedule against quantity and length mix at quotation.
Related knowledge
- What Bolt Property Classes 8.8, 10.9 and 12.9 Encode — and When High Strength Stops Being the Right Choice
- Bolt Grade Selection: ISO 898-1 8.8/10.9/12.9 vs ASTM A307 and A325
- 8.8 vs 10.9 vs 12.9 Bolts: Strength, Hardness and Cost — What the Evidence Settles
- Calculating Bolt Preload and Clamp Force: Torque, Friction and Tightening Method
- How to Determine Tightening Torque and Choose a Tightening Method for a Bolted Joint
- Fastener Failure Modes: Which Fatigue, Creep and SCC Controls the Evidence Supports
- Hydrogen Embrittlement in High-Strength Bolts: Which Grades Need Controls, Which Coatings and Baking Schedules Are Acceptable, and What to Require Before the RFQ
Request a Quote
Get factory-direct pricing from the manufacturer.
What to include in your inquiry
- ✓ Standard and property class (e.g. DIN 912, ISO 4762, class 8.8) — or a drawing for custom parts.
- ✓ Sizes, lengths and thread type (metric or inch).
- ✓ Quantity per size and your target delivery date.
- ✓ Destination country, plus any coating or finish requirement.
- ✓ Any documents you need with the shipment (e.g. mill test certificate) so the quote includes them.
- ✓ Your inquiry goes straight to the factory team by email and gets a reply within 24 hours.
- ✓ Factory-direct pricing
- ✓ Standard and custom specifications
- ✓ Factory-direct export to buyers in Europe, Asia, the Americas and the Middle East
- ✓ Full fastener family support