The 8UN (Серия 8 ниток на дюйм) is a constant-pitch thread standard within the Unified Thread Standard (UTS) family, governed автор ASME B1.1. Unlike UNC and UNF — where TPI changes with diameter — every 8UN thread from 1-1/16″ to 6″ uses exactly 8 ниток на дюйм. This reference страница provides the complete dimensional data you need for design, machining, and Осмотр.
At BravoFabs, we machine 8UN threads daily on CNC lathes for oil & gas flanges, pressure vessel studs, and heavy machinery components. This data is compiled from ASME B1.1 and verified against our Производство experience.
Ключевые выводы
- 8UN = constant 8 TPI across all diameters — one threading insert can machine multiple sizes
- Диаметр range: 1-1/16″ through 6″ per ASME B1.1 Table 2 (selected sizes also defined above 6″)
- Thread form: 60° V-thread with 0.125″ pitch (1/8″ per thread), flat root per UN profile
- Pitch diameter tolerance available in classes 2A/2B (general) and 3A/3B (precision)
- Primary industries: oil & gas (API flanges), Сосуды под давлением (ASME B16.5), heavy equipment, marine propulsion
8UN Полные данные по диаметру и шагу (ASME B1.1)
| Nominal Диаметр | TPI | Шаг (дюймы) | Basic Minor Ø Internal (in) | Basic Minor Ø External (in) | Метчик для нарезания резьбы (дюймы) |
|---|---|---|---|---|---|
| 1-1/16″ | 8 | 0.125 | 0.9375 | 0.9102 | 15/16 (0.9375) |
| 1-3/16″ | 8 | 0.125 | 1.0625 | 1.0352 | 1-1/16 (1.0625) |
| 1-5/16″ | 8 | 0.125 | 1.1875 | 1.1602 | 1-3/16 (1.1875) |
| 1-7/16″ | 8 | 0.125 | 1.3125 | 1.2852 | 1-5/16 (1.3125) |
| 1-9/16″ | 8 | 0.125 | 1.4375 | 1.4102 | 1-7/16 (1.4375) |
| 1-11/16″ | 8 | 0.125 | 1.5625 | 1.5352 | 1-9/16 (1.5625) |
| 1-13/16″ | 8 | 0.125 | 1.6875 | 1.6602 | 1-11/16 (1.6875) |
| 2″ | 8 | 0.125 | 1.8750 | 1.8477 | 1-7/8 (1.8750) |
| 2-1/4″ | 8 | 0.125 | 2.1250 | 2.0977 | 2-1/8 (2.1250) |
| 2-1/2″ | 8 | 0.125 | 2.3750 | 2.3477 | 2-3/8 (2.3750) |
| 2-3/4″ | 8 | 0.125 | 2.6250 | 2.5977 | 2-5/8 (2.6250) |
| 3″ | 8 | 0.125 | 2.8750 | 2.8477 | 2-7/8 (2.8750) |
| 3-1/4″ | 8 | 0.125 | 3.1250 | 3.0977 | 3-1/8 (3.1250) |
| 3-1/2″ | 8 | 0.125 | 3.3750 | 3.3477 | 3-3/8 (3.3750) |
| 3-3/4″ | 8 | 0.125 | 3.6250 | 3.5977 | 3-5/8 (3.6250) |
| 4″ | 8 | 0.125 | 3.8750 | 3.8477 | 3-7/8 (3.8750) |
| 4-1/4″ | 8 | 0.125 | 4.1250 | 4.0977 | 4-1/8 (4.1250) |
| 4-1/2″ | 8 | 0.125 | 4.3750 | 4.3477 | 4-3/8 (4.3750) |
| 5″ | 8 | 0.125 | 4.8750 | 4.8477 | 4-7/8 (4.8750) |
| 5-1/2″ | 8 | 0.125 | 5.3750 | 5.3477 | 5-3/8 (5.3750) |
| 6″ | 8 | 0.125 | 5.8750 | 5.8477 | 5-7/8 (5.8750) |
Note: Basic minor diameter for internal threads = nominal – 1.125 × pitch. For external threads, the basic minor diameter includes the thread root truncation per ASME B1.1 Figure 2. Tap drill sizes are for approximately 75% thread engagement — adjust for material and Применение.
Допуски диаметра шага резьбы 8UN (классы 2A/2B и 3A/3B)
Pitch diameter is the most critical dimension for thread fit. For 8UN threads at 8 TPI, the pitch diameter tolerance per ASME B1.1 is:
| Tolerance Class | Применение | PD Tolerance (8 TPI) | Типичное применение |
|---|---|---|---|
| 2A (External) | General industrial | 0.0089″ | Standard studs, bolts |
| 2B (Internal) | General industrial | 0.0106″ | Standard nuts, tapped holes |
| 3A (External) | точность / aerospace | 0.0057″ | High-precision studs |
| 3B (Internal) | точность / aerospace | 0.0069″ | Aerospace nuts,精密螺纹 |
For oil & gas Применениеs, most specifications call for Class 2A on studs and Class 2B on nuts. Class 3A/3B is reserved for Применениеs where thread fit must be controlled to prevent fatigue crack initiation — such as rotating equipment shafts and aerospace fasteners.
Зацепление резьбы 8UN: требования к минимальной длине
For full-strength thread engagement (bolt breaking before thread stripping), the minimum engagement length depends on the material combination:
| Nut Материал | Bolt Материал | Min Engagement (× diameter) | Min Engagement at 1-5/16″-8UN |
|---|---|---|---|
| Steel | Steel | 0.8D | 1.05″ |
| Steel | Алюминий | 1.5D | 1.97″ |
| Алюминий | Steel | 2.0D | 2.63″ |
| Cast Iron | Steel | 1.0D | 1.31″ |
| Stainless (304) | Stainless (304) | 1.2D | 1.58″ |
At 8 TPI, each full turn advances the bolt 0.125″. For a 1-5/16″-8UN steel nut on a steel stud, you need approximately 9 full turns for full-strength engagement. Less engagement = risk of thread stripping before bolt fracture.
Распространенные отрасли и применения резьбы 8UN
| Industry | Применение | Governing Standard |
|---|---|---|
| Oil & Gas | API 6A flanges, wellhead studs, BOP bonnet bolts | API 6A, ASME B16.5 |
| Сосуды под давлением | Heat exchanger studs, manway bolts, vessel flange bolting | ASME BPVC Section VIII, ASME B16.5 |
| Heavy Оборудование для контроля качества, которое мы используем ежедневно | Hydraulic cylinder end caps, track pin retainers | Manufacturer spec (CAT, Komatsu) |
| Marine | Propeller shaft nuts, rudder stock bolts, hatch dog bolts | Classification society (ABS, DNV, LR) |
| Power Generation | Turbine casing studs, steam valve bonnet bolts | ASTM A193, ASTM A453 |
| Aerospace | Landing gear bolts, engine mount studs | ASME B1.1, AMS specs |
8UN Резьба: Параметры настройки CNC
For CNC lathe single-point threading of 8UN threads, we use the following starting parameters (adjust for material and insert grade):
| Parameter | Алюминий (6061) | Углеродистая сталь (1018/1045) | Stainless (304/316) | Alloy Steel (4140) |
|---|---|---|---|---|
| Cutting Speed (SFM) | 300-500 | 200-350 | 150-250 | 150-250 |
| Number of Passes | 8-12 | 12-16 | 14-18 | 14-20 |
| Infeed per Pass | 0.015″ → 0.002″ | 0.012″ → 0.001″ | 0.010″ → 0.001″ | 0.010″ → 0.0005″ |
| Infeed Method | Modified flank | Modified flank | Modified flank | Radial (for hardness) |
| Insert Grade | Uncoated carbide | PVD TiAlN | PVD TiAlN | CVD Al₂O₃ |
| Coolant | Soluble oil (5-8%) | Soluble oil (8-10%) | Heavy-duty (10-12%) | Heavy-duty (10-12%) |
Note on 8UN vs UNC tooling: Because 8UN is constant 8 TPI across all diameters, a single 8 TPI full-profile threading insert can machine any 8UN diameter — no insert changes between sizes. This is a significant Производство advantage for shops that machine multiple 8UN diameters in the same setup.
Контрольный список резьбы 8UN
Every 8UN threaded part we produce at BravoFabs is verified against this checklist:
- Go/No-Go thread plug gauge (internal) or thread ring gauge (external) — primary acceptance test
- Оптический компаратор at 20× — verify 60° thread angle, root radius, crest flatness
- Three-wire pitch diameter measurement — for precision Class 3A/3B threads, measured to ±0.0002″
- . Проверка включает: under magnification — check for torn threads, burrs, chatter marks
- Материал certification review — verify heat number and material grade match the PO requirements
- Thread protector installation — for finished studs shipping to site, prevent handling damage
For more on thread series selection and interchangeability, see our guides on UNC vs UNF vs 8UN comparison, UNC and 8UN interchangeability rules, and CNC thread manufacturing methods.
Советы инженерам по проектированию резьбы 8UN
Укажите полное обозначение резьбы на чертежах
A complete 8UN thread callout on an engineering drawing should include: nominal diameter, threads per inch, series designation, tolerance class, and any special requirements. Example: “1-5/16-8UN-2A” tells the machinist everything needed — diameter, TPI, series, and fit class. Ambiguous callouts like “8UN thread” or “8 TPI” without a diameter and tolerance class will result in questions from the shop, adding 1-2 days to your quote turnaround.
Выберите правильный класс допуска: 2A/2B против 3A/3B
For 95% of industrial Применениеs, Class 2A (external) and 2B (internal) are sufficient. These provide a running fit with adequate clearance for assembly and are the default for oil & gas studs and nuts. Reserve Class 3A/3B for Применениеs where thread fit directly affects fatigue life — rotating shafts, aerospace fasteners, and精密定位螺纹. Class 3 adds roughly 15-25% to machining cost due to tighter Осмотр requirements. If you are unsure which class to specify, see our thread selection decision guide for a step-автор-step framework.
Выбор материала для деталей с резьбой 8UN
8UN threads are most commonly machined in 4140/4142 alloy steel (ASTM A193 B7 for studs, ASTM A194 2H for nuts), 304/316 Нержавеющая сталь (ASTM A193 B8/B8M for corrosive service), and 17-4 PH stainless (ASTM A564 for high-strength corrosive Применениеs). For non-pressure Применениеs, 1018/1045 Углеродистая сталь with цинкование is the economical choice. Алюминий 8UN threads are rare — at large diameters, aluminum lacks the thread strength needed for high-torque assembly. If weight reduction is critical, consider a steel threaded insert in an aluminum body.
Лучше всего для 8UN: 4140 heat-treated to 22-32 HRC — balances machinability with thread strength. Avoid: Unalloyed aluminum above 1″ diameter — thread stripping risk exceeds acceptable margins at typical 8UN torque values.
Нужна резьба 8UN? Получите расценки с полным обзором спецификаций
BravoFabs produces custom 8UN threaded components from 1-1/16″ to 6″ diameter in Углеродистая сталь, stainless, alloy steel, and aluminum. We provide full thread Осмотр reports with Каждая партия — Go/No-Go gauge results, Оптический компаратор images, and material certifications.
Upload your drawing with the complete thread callout (e.g., “2-1/2-8UN-2A, ASTM A193 B7, with 3.1 material cert”). We’ll confirm the machining plan and Осмотр criteria in your quote. Запросить предложение →
Нужны детали с резьбой 8UN? Бесплатные расценки CNC с обзором чертежей
Отправить us your drawing or STEP file and we’ll provide a detailed machining quote — including material recommendations, thread Осмотр plan, and delivery timeline. ISO-certified, serving industrial clients in DE/US/CA/EU.
🔗 Related Thread & Manufacturing Ресурсы
- 8UN vs UNC Thread Серия: Complete Comparison Руководство — pillar reference
- Can UNC Replace 8UN? Thread Interchangeability Руководство — bolt substitution rules
- UNC vs UNF vs 8UN: Thread Selection Руководство — decision framework for engineers
- Как изготовить резьбу в металлообработке — CNC threading methods
- Услуги токарной обработки с ЧПУ — single-point threading for shafts and cylindrical parts
