Machine Screw Nut Sizes and Dimensions Chart according to ASME B18.6.3-2003 standard.
Machine screw hex nut is a hexagonal shape fastener which is used with a machine
screw to fix parts together.
Some important notes from the ASME B18.6.3:
- The diameter range of machine screw nuts is from 0.0600 inch to 0.3750 inch
according to standard.
- Threads shall be Unified inch coarse or fine with tolerance class of 2B (UNC or UNF).
- Machine screw nuts are generally supplied in steel, stainless steel, or brass as specified by the purchaser.
Unless otherwise specified, no physical requirements shall apply
Note 1: Hexagon machine screw nuts shall have top and bottom surfaces flat, with chamfered corners. The flat surface diameters shall be equal to the maximum width across flats, with a tolerance of minus 15%.
The bearing surface shall be perpendicular to the axis of the threaded hole pitch cylinder within a tolerance of 4 deg.
Note 2: Bottoms of hexagon machine screw nuts may be supplied with flat, but unchamfered surfaces at the option of the manufacturer.
Gages and Gauging : Specifications and dimensions for the gages used on Unified inch screw thread is defined in the ANSI/ASME B1.2-1983 standard.
Types of gages including thread plug gages, snap gages, thread ring gages and
plain diameter gages for internal and external threads are covered in same
standard. Screw thread gauging systems for acceptability is covered in the ASME
Details of gages and gauging about the machine screws heads are given in the
appendices of the ASME B18.6.3-2003 standard.
Unified Screw Thread: A thread
form used by the United Kingdom, Canada, and the United States to obtain screw
thread interchangeability among these three nations. It has 60° thread angle and
dimensions are stated in inch units.
UN form screw threads: The UN
thread is intended for general purpose fastening operations.
UNC (Unified National Coarse):
Most commonly used type for general engineering applications. This thread form
is used in materials with low tensile strength which makes threads more
resistance against stripping (internal threads) .UNC give possibility for quick assembly.
UNF (Unified National Fine): External
threads of this Fine Series have greater tensile stress area than comparable sizes of the
coarse series. The Fine series is suitable when the resistance to stripping of both external
and mating internal threads equals or exceeds the tensile load carrying capacity of the
externally threaded member. It is also used where the length of engagement
is short, where a smaller lead angle is desired, where the wall thickness demands a fine
pitch, or where finer adjustment is needed.
Thread class: A classification system to classify the threads for
interchangeability and manufacturability. Class 1 threads are loosely fitting
thread and used for ease of assembly. Most commonly used class is 2 and this
class is designed for general use. Class 3 is used for closer tolerances.