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THREAD PITCH CHART (UNC / UNF / UNEF / UN)

The chart below lists threads per inch (TPI) for UNC, UNF, UNEF, and constant-pitch UN series (4-UN, 6-UN, 8-UN, 12-UN, 16-UN, 20-UN, 28-UN, 32-UN) up to 2 inches, per ASME B1.1 Unified Inch Screw Threads.

Thread pitch chart — ASME B1.1 (up to 2 in)
Thread pitch chart
Threads per inch (TPI) Nominal
Size, in.
Series with graded pitches Series with constant pitches
Nominal Size, in. Basic Major
Diameter		 UNC UNF UNEF 4-UN 6-UN 8-UN 12-UN 16-UN 20-UN 28-UN 32-UN
Primary Secondary in TPI TPI TPI TPI TPI TPI TPI TPI TPI TPI TPI
0—0.0600—80 UNF—————————0
—10.073064 UNC72 UNF—————————1
2—0.086056 UNC64 UNF—————————2
—30.099048 UNC56 UNF—————————3
4—0.112040 UNC48 UNF—————————4
5—0.125040 UNC44 UNF—————————5
6—0.138032 UNC40 UNF—————————6
8—0.164032 UNC36 UNF—————————8
10—0.190024 UNC32 UNF—————————10
—120.216024 UNC28 UNF32 UNEF——————283212
1/4—0.250020 UNC28 UNF32 UNEF—————2028321/4
5/16—0.312518 UNC24 UNF32 UNEF————162028325/16
3/8—0.375016 UNC24 UNF32 UNEF————162028323/8
7/16—0.437514 UNC20 UNF28 UNEF————162028327/16
1/2—0.500013 UNC20 UNF28 UNEF————162028321/2
9/16—0.562512 UNC18 UNF24 UNEF———12162028329/16
5/8—0.625011 UNC18 UNF24 UNEF———12162028325/8
—11/160.6875——24 UNEF———121620283211/16
3/4—0.750010 UNC16 UNF20 UNEF———12162028323/4
—13/160.8125——20 UNEF———121620283213/16
7/8—0.87509 UNC14 UNF20 UNEF———12162028327/8
—15/160.9375——20 UNEF———121620283215/16
1—1.00008 UNC12 UNF20 UNEF——812162028321
—1-1/161.0625——18 UNEF——812162028—1-1/16
1-1/8—1.12507 UNC12 UNF18 UNEF—6812162028—1-1/8
—1-3/161.1875——18 UNEF—6812162028—1-3/16
1-1/4—1.25007 UNC12 UNF18 UNEF—6812162028—1-1/4
—1-5/161.3125——18 UNEF—6812162028—1-5/16
1-3/8—1.37506 UNC12 UNF18 UNEF—6812162028—1-3/8
—1-7/161.4375——18 UNEF—6812162028—1-7/16
1-1/2—1.50006 UNC12 UNF18 UNEF—6812162028—1-1/2
—1-9/161.5625——18 UNEF—68121620——1-9/16
1-5/8—1.6250——18 UNEF—68121620——1-5/8
—1-11/161.6875——18 UNEF—68121620——1-11/16
1-3/4—1.75005 UNC———68121620——1-3/4
—1-13/161.8125————68121620——1-13/16
1-7/8—1.8750————68121620——1-7/8
—1-15/161.9375————68121620——1-15/16
2—2.00004 1/2 UNC———68121620——2

Series Differences & Typical Applications

  • UNC: General machinery and MRO; faster assembly, less risk of thread damage in harsh conditions.
  • UNF: Automotive and aerospace; higher clamp accuracy and better vibration resistance.
  • UNEF: Thin-walled parts and instrumentation; reliable grip with short engagement length.
  • Constant-pitch UN: Standardized TPI across larger diameters for consistent assembly.

Practical Tips

  • Choose the thread series considering material, load, vibration, and assembly environment—not just TPI.
  • Fine pitches (UNF/UNEF) are more sensitive to debris and galling—ensure clean, lubricated assembly where required.
  • Apply tightening torque per fastener grade and manufacturer recommendations.

Reference

  • ASME B1.1 — Unified Inch Screw Threads (UN and UNR Thread Form)

Frequently Asked Questions

UNC or UNF? Use UNC for general purpose and faster assembly; use UNF for higher clamp accuracy and vibration resistance.

When to use UNEF? For thin-walled parts, short engagement length, or when precise adjustment is required.