What does AF mean on an orthographic drawing?

On an orthographic drawing, AF is an abbreviation that stands for "across flats". This dimension is crucial for specifying the size of components, particularly those with a polygonal cross-section, such as hexagonal or square parts.

Understanding 'Across Flats' (AF) in Detail

"Across flats" refers to the distance measured between two parallel flat surfaces on a component. Unlike a diameter, which measures across the widest point of a circular object, AF specifically defines the dimension for non-circular, multi-sided shapes. It is most commonly associated with:

• Hexagonal components: Such as nuts, bolts, and bolt heads.
• Square components: Like square head bolts or certain key stock.
• Other polygonal shapes: Where a specific measurement between parallel sides is critical.

This measurement is essential for ensuring that the correct tools, like wrenches or sockets, can be used to fasten or unfasten the part. It also plays a vital role in manufacturing processes, as it dictates the size of the raw material stock required or the setup for machining operations.

Importance and Application in Engineering Drawings

Specifying the "across flats" dimension precisely on an orthographic drawing provides critical information for fabrication, assembly, and maintenance.

• Tool Compatibility: The AF dimension directly correlates to standard wrench sizes. For example, a hexagonal nut with an AF dimension of 19mm requires a 19mm wrench.
• Material Selection: Manufacturers use the AF dimension to select appropriate bar stock for machining components.
• Fit and Clearance: It ensures proper fit with mating parts or within confined spaces where specific clearances are necessary.
• Quality Control: During inspection, the AF measurement is a key parameter for verifying part conformity to design specifications.

Common Contexts for AF on Drawings

You will frequently encounter the "AF" abbreviation in the following scenarios on engineering drawings:

• Fasteners: Dimensions for hex nuts, hex bolts, and cap screws will often include an AF specification.
• Shaft Features: A shaft might have a section with "wrench flats" – parallel flat surfaces machined onto a round shaft, allowing it to be gripped by a wrench. The AF dimension defines these flats.
• Tooling Components: Jaws, fixtures, or other tooling parts that need to grip or hold polygonal workpieces will be dimensioned with AF.

Key Engineering Drawing Abbreviations

Understanding common abbreviations is fundamental to interpreting orthographic and other technical drawings. Here are a few examples, including AF:

In summary, when you see "AF" on an orthographic drawing, it precisely indicates the measurement between parallel flat surfaces on a component, vital for tool fitting, manufacturing, and overall design integrity.