# ASME/ANSI BUTTRESS INCH THREAD DIMENSIONS CHART AND CALCULATOR

ANSI/ASME buttress thread chart calculator for buttress thread with load angle of 7 degrees and a clearance angle of 45 deg from the normal to the axis. The basic height of thread engagement for buttress thread is 0.6p. The buttress thread form has certain advantages for the applications where high stress occurs only in one direction along the thread axis. The buttress form of thread is particularly applicable when tubular members screwed together. Breech assemblies of large guns, airplane propeller hubs and columns for hydraulic presses are some of the examples of buttress threaded rods and nuts.

Buttress thread calculator is according to ANSI B1.9-1973 “Buttress Inch Screw Threads” standard. The standard provides information about preferred diameter-pitch combinations, formulas for calculation pitch diameter tolerances, tolerances for major and minor diameters, a system of allowances between external and internal threads, recommended methods of measuring and gauging, dimensional acceptability of buttress threaded rods and nuts.

 INPUT PARAMETERS Nominal diameter (inches) - threads per inch 1/2-12 1/2-16 1/2-20 5/8-12 5/8-16 5/8-20 3/4-12 3/4-16 3/4-20 7/8-10 7/8-12 7/8-16 1-10 1-12 1-16 1 1/4-8 1 1/4-10 1 1/4-12 1 3/8-8 1 3/8-10 1 3/8-12 1 1/2-8 1 1/2-10 1 1/2-12 1 3/4-6 1 3/4-8 1 3/4-10 2-4 2-6 2-8 2-10 2 1/4-6 2 1/4-8 2 1/4-10 2 1/2-6 2 1/2-8 2 1/2-10 2 3/4-5 2 3/4-6 2 3/4-8 3-5 3-6 3-8 3 1/2-5 3 1/2-6 3 1/2-8 4-5 4-6 4-8 4 1/2-4 4 1/2-5 4 1/2-6 5-4 5-5 5-6 5 1/2-4 5 1/2-5 5 1/2-6 6-4 6-5 6-6 Thread Tolerance Class 1 Class 2 Class 3

Note: 1 Tolerance on major diameter of external thread, pitch diameter of external and internal thread, and minor diameter of internal thread.

### Definitions:

Gages for Buttress Screw Threads: Recommended gages and gauging practice for external and internal buttress thread are defined in ASME B1.9 standard. Gage maker's tolerances, gages for buttress threaded rods and nuts including GO/NOT GO plain ring gages, threaded rings, setting plug gages and necessary information related with gauging is given in this standard.

Allowance: An allowance (clearance) should be provided on all external threads to secure easy assembly of parts.

Major Diameter: The maximum diameter of a thread which is diameter of the crest of a male thread or root of a female thread.

Minor Diameter: The minimum diameter of a thread which is diameter of the root of a male thread or crest of a female thread.

Roots of Threads: There are 2 alternatives for thread roots. These are rounded and flat roots.

Rounded Roots: Equal radii, at the roots of the external and internal basic thread forms tangential to the load flank and the clearance flank. The rounded root form of the external and internal thread shall be a continuous, smoothly blended curve within the zone defined by 0.07141p maximum to 0.0357p minimum radius. The resulting curve shall have no reversals and sudden angular variations, and shall be tangent to flanks of the thread. There is, in practice, almost no chance that the thread forms will be achieved strictly as basically specified, that is, as true radii.

Standard 7° / 45° Buttress Thread with 0.6p Basic Height of Thread Engagement and Round Root

Flat Roots: Equal flat root of the external and internal thread. In instances where absence of root radius is not detrimental to the requirements for strength, and where it is more economical to provide tools which do not produce a radius at root, flat root buttress threads may be specified.

Standard 7° / 45° Buttress Thread with 0.6p Basic Height of Thread Engagement and Flat Root

Threads designation: When only the designation, BUTT is used, the thread is "pull" type buttress (external thread pulls) with the clearance flank leading and the pressure flank 7° following. When the designation, PUSH-BUTT is used, the thread is a push type buttress (external thread pushes) with the load flank 7° leading the 45° clearance flank following.