Acme Thread Dimensions — ASME B1.5 General-Purpose 2G Limits of Size (1/4-16 to 5-2, inch)
Limits of size for general-purpose Acme screw threads per ASME B1.5 — 23 designations from 1/4-16 to 5-2 at class 2G, each with major, pitch and minor diameter max/min, transcribed row-for-row from the collected chart.
Last updated: 2026-11
Specifications
Acme is the workhorse power-transmission thread: the 29° trapezoidal form that runs leadscrews, lathe cross-slides, presses, valve stems and jack screws — anything that turns rotary motion into heavy linear motion. The collected chart prints what a shop needs to accept or cut a general-purpose Acme thread: for each of the 23 designations — 1/4-16, 1/2-10, 3/4-6, 1-5, 1 1/4-5 up through 4 1/2-2 and 5-2 — the major, pitch and minor diameter maximum and minimum at class 2G, the standard general-purpose fit with its built-in clearance. Reading rows: 1/4-16 runs a major of 0.2500/0.2450, pitch diameter 0.2148/0.2043 and minor 0.1775/0.1618 in; 1-5 runs 1.0000/0.9900 major, 0.8920/0.8726 pitch; at the coarse end 5-2 allows 5.0000/4.9750 major with a pitch window of 4.7319/4.6973 in. The pitch-diameter window is the operating figure — it is what a thread mic or the three-wire method checks, because flank fit there decides both running friction and backlash; the major/minor columns carry the crest and root clearance that keep the flat-thread flanks, not the corners, doing the work. Two reading notes carried from the source: rows are printed in lexicographic order rather than by size (flagged on the table — re-sort if you read it as a ladder), and the chart tabulates class 2G only; centralizing Acme fits and other classes are not covered here. Material, lead accuracy over length and surface finish are RFQ decisions, not chart lookups.
| Standard | ASME B1.5 — Acme screw threads, general-purpose; 2G class limits of size, 23 designations 1/4-16 to 5-2 (4 to 2 TPI across the range) |
|---|---|
| Per-row data (in) | Major, pitch and minor diameter max/min at class 2G — examples: 1/4-16 → pitch 0.2148/0.2043; 1-5 → pitch 0.8920/0.8726; 5-2 → pitch 4.7319/4.6973 |
| Class coverage | 2G general-purpose only; centralizing Acme and other tolerance classes are not tabulated by the collected chart — per RFQ (state class with the size) |
| Row order | Source rows in lexicographic order (1 1/2-4 before 1 1/4-5), not by size — reproduced as printed, flagged on the table |
| Lead accuracy / material / finish | Not tabulated — per RFQ (state leadscrew application, length, and mating nut type together) |
| Size | TPI | Class | Major Dia. Max (in) | Major Dia. Min (in) | Pitch Dia. Max (in) | Pitch Dia. Min (in) | Minor Dia. Max (in) | Minor Dia. Min (in) |
|---|---|---|---|---|---|---|---|---|
| 1 1/2-4 | 4 | 2G | 1.5000 | 1.4875 | 1.3652 | 1.3429 | 1.2300 | 1.1965 |
| 1 1/4-5 | 5 | 2G | 1.2500 | 1.2400 | 1.1411 | 1.1210 | 1.0300 | 0.9998 |
| 1 1/8-5 | 5 | 2G | 1.1250 | 1.1150 | 1.0165 | 0.9967 | 0.9050 | 0.8753 |
| 1 3/4-4 | 4 | 2G | 1.7500 | 1.7375 | 1.6145 | 1.5916 | 1.4800 | 1.4456 |
| 1 3/8-4 | 4 | 2G | 1.3750 | 1.3625 | 1.2406 | 1.2186 | 1.1050 | 1.0720 |
| 1-5 | 5 | 2G | 1.0000 | 0.9900 | 0.8920 | 0.8726 | 0.7800 | 0.7509 |
| 1/2-10 | 10 | 2G | 0.5000 | 0.4950 | 0.4443 | 0.4306 | 0.3800 | 0.3594 |
| 1/4-16 | 16 | 2G | 0.2500 | 0.2450 | 0.2148 | 0.2043 | 0.1775 | 0.1618 |
| 2 1/2-3 | 3 | 2G | 2.5000 | 2.4833 | 2.3207 | 2.2939 | 2.1467 | 2.1065 |
| 2 1/4-3 | 3 | 2G | 2.2500 | 2.2333 | 2.0713 | 2.0450 | 1.8967 | 1.8572 |
| 2 3/4-3 | 3 | 2G | 2.7500 | 2.7333 | 2.5700 | 2.5427 | 2.3967 | 2.3558 |
| 2-4 | 4 | 2G | 2.0000 | 1.9875 | 1.8637 | 1.8402 | 1.7300 | 1.6948 |
| 3 1/2-2 | 2 | 2G | 3.5000 | 3.4750 | 3.2350 | 3.2026 | 2.9800 | 2.9313 |
| 3-2 | 2 | 2G | 3.0000 | 2.9750 | 2.7360 | 2.7044 | 2.4800 | 2.4326 |
| 3/4-6 | 6 | 2G | 0.7500 | 0.7417 | 0.6598 | 0.6424 | 0.5633 | 0.5372 |
| 3/8-12 | 12 | 2G | 0.3750 | 0.3700 | 0.3284 | 0.3161 | 0.2817 | 0.2632 |
| 4 1/2-2 | 2 | 2G | 4.5000 | 4.4750 | 4.2330 | 4.1991 | 3.9800 | 3.9291 |
| 4-2 | 2 | 2G | 4.0000 | 3.9750 | 3.7340 | 3.7008 | 3.4800 | 3.4302 |
| 5-2 | 2 | 2G | 5.0000 | 4.9750 | 4.7319 | 4.6973 | 4.4800 | 4.4281 |
| 5/16-14 | 14 | 2G | 0.3125 | 0.3075 | 0.2728 | 0.2614 | 0.2311 | 0.2140 |
| 5/8-8 | 8 | 2G | 0.6250 | 0.6188 | 0.5562 | 0.5408 | 0.4800 | 0.4570 |
| 7/16-12 | 12 | 2G | 0.4375 | 0.4325 | 0.3909 | 0.3783 | 0.3442 | 0.3253 |
| 7/8-6 | 6 | 2G | 0.8750 | 0.8667 | 0.7842 | 0.7663 | 0.6883 | 0.6615 |
- Row 1 (1 1/2-4): Source row order is lexicographic, not by size (e.g. 1 1/2-4 precedes 1 1/4-5; 5/16-14 follows 5-2) — all 23 designations 1/4-16 through 5-2 present; reproduced as printed.
- Row 23 (7/8-6): The lexicographic order scatters the ladder (5/16-14 and 7/8-6 close the table while 4 1/2-2 and 5-2 — the 2-TPI coarse end of the range — sit mid-table); sizes 1/4-16 through 5-2 all present, 23 designations.
Materials
- Acme threaded parts run in steel, stainless and bronze-matched pairs; the chart is form-and-fit data and is material-independent. State the workpiece alloy and mating nut material 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 (Acme Thread Dimensions — ASME B1.5 General-Purpose 2G Limits of Size (1/4-16 to 5-2, inch)) 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 10,000 pieces. Stock items run 3–7 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 is the pitch-diameter window the figure that matters on an Acme thread, and what does class 2G buy me?
On a power thread the flanks do the work, and the flanks meet at the pitch diameter — so the 2G window printed there (e.g. 0.2043 to 0.2148 in on 1/4-16) is the dimension that decides how the nut rides the screw: near its maximum the assembly runs loose with clearance for lubricant and thermal growth, near its minimum the fit tightens and backlash shrinks, at the cost of running torque. The major and minor columns matter as envelope guards, not as fit surfaces — crest and root must stay clear of each other, which the Acme form guarantees by design once the pitch diameter is inside class. 2G is the general-purpose fit the standard defines for the common case: a screw and nut with default clearance, gaged with the standard GO/NO-GO stack. What the chart cannot decide: whether your application wants a tighter bespoke fit (a lathe cross-slide may), a centralizing fit that controls the major-diameter clearance instead (a different B1.5 class, not tabulated here), the lead accuracy over the screw length, or the material pairing against wear — those are application and process calls, so state the application, screw length and nut type at RFQ.
What is the MOQ and lead time for threaded parts and tooling referenced by this chart?
The minimum order quantity is 10,000 pieces. Stock items ship in 3–7 days; non-stock items are confirmed at quotation. Confirm the exact schedule against quantity, size mix and any tooling items at quotation.
Related knowledge
- Thread-Forming vs Thread-Cutting vs Thread-Rolling Self-Tapping Screws: What the Evidence Settles on Base Material
- Screw Family Selection by Base Material: Wood, Machine and Self-Tapping Threads, Engagement and Coating
- Hex Bolts vs Socket Head Cap Screws: What the Evidence Settles on Strength, Clearance and Cost
Request a Quote
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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