Button head socket cap screw dimensions are shown in the following chart according to ASME B18.3-2003 standard.
Button head cap screw is a type of cap screw which is recommended for lighter fastening operations. It's not suggested for use in critical high strength applications where socket head cap screws should normally used.
Some important notes from the ASME B18.3:
- The diameter range of button head cap screws is from 0.0600 inch to 0.6250 inch according to standard.
- Thread shall conform to Unified external threads with radius root: Class 3A UNRC and UNRF for screw sizes No. 0 through 1 inch inclusive.
- Alloy steel cap screws shall conform to ASTM F835 and stainless steel cap screws shall conform to ASTM F879.
Note1: The tolerance on the unthreaded portion of the screw.
Note2: For screws of nominal lengths equal to or shorter than standard maximum lengths L given, the complete (full-form) threads shall extend to within two pitches (threads) of the bearing surface of the head. For longer screws, the length of the complete thread shall, at the option of the screw manufacturer, be between the minimum limit of twice the basic screw diameter plus 0.50 in. and the maximum limit within two pitches (threads) of the head.
Note3: The form of the fillet shall be optional, provided it flairs into the bearing surface between the minimum and maximum diameter F.
Designation: Product Name, Designation of the Standard, Nominal Size - Thread Pitch x Nominal Length, Material, Protective Finish (if required) Ex: Hexagon Socket Button Head Cap Screws, ASME B18.3, 8 - 32 x 0.75, Alloy Steel, Zinc Plated
Long Screw (Full Body Screw): Screw which is not threaded for full length.
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.
Short Screw (Thread to Head Screw): A screw which is threaded for full length.
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.
Thread 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.