# ASME UN SCREW THREAD AND TOLERANCE CALCULATOR

ASME UN screw thread calculator to calculate imperial unified screw thread basic major, minor, pitch diameters and thread tolerance for the external (bolt) and internal (nut) inch threads according to ASME B1.1 standard.

- UN and UNR thread forms

- Standard series of UNC, UNF, UNEF, UN-4, UN-6, UN-8, UN-12, UN-16, UN-20, UN-28 and UN-32.

- Tolerance classes of 1A, 2A and 3A for bolts and 1B, 2B and 3B for nuts

- Thread size from 0.0600 inch to 2 inches

Tolerance class 2A and class 2B are selected classes for commercial external and internal threads per ASME B1.1. The user shall use class 2A for bolts and 2B for nuts unless there is a specific requirement to use other tolerance classes.

Dimensions given by this calculator are at 68 °F.

### UN Unified Screw Thread Calculator:

 INPUT PARAMETERS Nominal Size in Inches and Threads per Inch 0-80 1-64 1-72 2-56 2-64 3-48 3-56 4-40 4-48 5-40 5-44 6-32 6-40 8-32 8-36 10-24 10-32 12-24 12-28 12-32 1/4-20 1/4-28 1/4-32 5/16-18 5/16-20 5/16-24 5/16-32 3/8-16 3/8-20 3/8-24 3/8-28 3/8-32 7/16-14 7/16-16 7/16-20 7/16-28 7/16-32 1/2-13 1/2-16 1/2-20 1/2-28 1/2-32 9/16-12 9/16-16 9/16-18 9/16-20 9/16-24 9/16-28 9/16-32 5/8-11 5/8-12 5/8-16 5/8-18 5/8-20 5/8-24 5/8-28 5/8-32 11/16-12 11/16-16 11/16-20 11/16-24 11/16-28 11/16-32 3/4-10 3/4-12 3/4-16 3/4-20 3/4-28 3/4-32 13/16-12 13/16-16 13/16-20 13/16-28 13/16-32 7/8-9 7/8-12 7/8-14 7/8-16 7/8-20 7/8-28 7/8-32 15/16-12 15/16-16 15/16-20 15/16-28 15/16-32 1-8 1-12 1-16 1-20 1-28 1-32 1 1/16-12 1 1/16-16 1 1/16-18 1 1/8-7 1 1/8-8 1 1/8-12 1 1/8-16 1 1/8-18 1 1/8-20 1 1/8-28 1 3/16-12 1 3/16-16 1 3/16-18 1 1/4-7 1 1/4-8 1 1/4-12 1 1/4-16 1 1/4-18 1 1/4-20 1 1/4-28 1 5/16-12 1 5/16-16 1 5/16-18 1 3/8-6 1 3/8-8 1 3/8-12 1 3/8-16 1 3/8-18 1 3/8-20 1 3/8-28 1 7/16-12 1 7/16-16 1 7/16-18 1 1/2-6 1 1/2-8 1 1/2-12 1 1/2-16 1 1/2-18 1 1/2-20 1 1/2-28 1 9/16-16 1 9/16-18 1 5/8-8 1 5/8-12 1 5/8-16 1 5/8-18 1 5/8-20 1 11/16-16 1 11/16-18 1 3/4-5 1 3/4-6 1 3/4-8 1 3/4-12 1 3/4-16 1 3/4-20 1 13/16-16 1 7/8-6 1 7/8-8 1 7/8-12 1 7/8-16 1 7/8-20 1 15/16-16 2-4.5 2-6 2-8 2-12 2-16 2-20 External Thread (Bolt) Tolerance Class * 1A 2A 3A Internal Thread (Nut) Tolerance Class ** 1B 2B 3B

Note : * 2A is normally selected for commercial external (bolt) threads. Use this tolerance class for commercial external (bolt) threads.

Note : ** 2B is normally selected for commercial internal (nut) threads. Use this tolerance class for commercial internal (nut) threads.

 RESULTS Parameter Value Nominal Size -- --- --- Threads per inch -- --- Tolerance Class for External Thread -- --- Tolerance Class for Internal Thread -- --- Series Designation -- --- LIMITS OF SIZES FOR EXTERNAL THREADS (BOLTS) Allowance es --- inch Maximum Major Diameter dmax --- Minimum Major Diameter dmin --- Maximum Pitch Diameter d2max --- Minimum Pitch Diameter d2min --- Maximum Minor Diameter d1max --- UNR Maximum Minor Diameter d3max --- Thread Callout --- LIMITS OF SIZES FOR INTERNAL THREADS (NUTS) Minimum Major Diameter Dmin --- inch Maximum Pitch Diameter D2max --- Minimum Pitch Diameter D2min --- Maximum Minor Diameter D1max --- Minimum Minor Diameter D1min --- Thread Callout --- BASIC DIMENSIONS Basic Major Diameter d , D --- inch Basic Pitch Diameter d2 , D2 --- Basic Minor Diameter d1 , D 1 --- UNR Reference Minor Diameter  for External threads d3 --- Fundamental Triangle Height H --- Lead Angle at Basic Pitch Dia. λ --- ---

Note-1: ASME B1.1-2003 specifies limits of size that pertain whether threads are coated or uncoated. Only in Class 2A threads is the allowance available to accommodate coatings. Thus, in all classes of internal threads and in all Classes 1A and 3A external threads, limits of size must be adjusted before plating to provide suitable provision for the desired coating.

Note-2: Unless otherwise specified, size limits for standard external thread Class 2A apply prior to coating. The external thread allowance may thus be used to accommodate the coating thickness on coated parts, provided that the maximum coating thickness is no more than one-fourth of the allowance.

Note 3: The minimum diameters of Class 1B, 2B and 3B threads, whether or not plated or coated, are basic and give no allowance or clearance for assembly at maximum-material limits.

### Reference:

• ASME B1.1-2003, Unified Inch Screw Threads (UN and UNR Thread Form)
• Oberg, E. , Jones ,F.D. , Horton H.L. , Ryffel H.H., (2016) . Machinery's Handbook . 30th edition.  Industrial Press Inc.
• Oberg, E. , Jones ,F.D. , Horton H.L. , Ryffel H.H., (2012) . Machinery's Handbook . 29th edition.  Industrial Press Inc.