Drafting Standards and the Genium Drafting Manual

Here, we take a drafting standard, briefly explain its background and what it addresses, and then show how it's treated in the Drafting Manual.

ASME Y14.6 – 2001, Screw Thread Representation

ASME Y14.6 - 2001, Screw Thread Representation is a standard for depicting screw threads on drawings and other documents. It does not cover engineering and manufacturing specifications for screw threads. This standard was originally approved on December 13, 1957 and was designated American Standards Association ASA Y14.6-1957. In 1969 it was re-designated ANSI Y14.6-1957 (note the dates). The next revision was July 26, 1978 (ANSI Y14.6-1978) with a metric supplement approved on September 21, 1981 and released as ANSI Y14.6aM-1981. This latest revision in 2001 revised and consolidated ANSI Y14.6-1978 and ANSI Y14.6aM-1981.

Throughout the history of this standard, technical support has been provided through liaison with societies such as the National Defense Industrial Association (NOIA) [formerly known as the American Defense Preparedness Association (ADPA)], Aerospace Industries Association (AIA), Electronic Industries of America (EIA), and the Society of Automotive Engineers (SAE).

The latest revision (2001) contains the following significant changes:

1. First of all it combines the metric standard (Y14.6aM-1981) and the decimal inch standard (Y14.6-1978).
2. It was updated in accordance with the latest issue of ASME B1 series.
3. For decimal inch sizes you should no longer put a zero in front of the decimal point. For example, under the old standard it would be 0.750, but in this revised standard it is .750.
4. For fractional decimal equivalents, you should reduce a fourth digit zero to three decimal places. For example, .7500 should be reduced to .750.
5. “Screw numbers” may be used to designate nominal thread size. However, fractional and decimal sizes are still permitted.
6. Thread gaging systems 21, 22 and 23, based on ASME B1.3M for inch and metric (UN, UNR, UNJ, M, and MJ), have been added to thread callouts. System 21 is the lowest level of gaging, system 22, the middle level, and system 23, the highest level. Generally if systems 22 and 23 are specified it will require new gaging equipment.

This standard is covered in Section 4.14 of the Genium Drafting Manual. This Section, titled Screw Thread Representation, provides the following:

1. Clear explanations and figures showing screw thread representation as covered in the standard.
2. A clear definition and discussion of gaging systems 21, 22, and 23.
3. A table showing the largest hole size for a specific fastener hex head size.
4. Easy to use GD&T formulas for position.
5. A discussion showing why a projected tolerance zone should be used.
6. A table of thread sizes for both inch and metric screw designations.

The DoD is now relying on the ASME B1 series for thread performance specifications, leaving the responsibility for design, processes, quality control, etc, to the thread manufacturer. These aspects are covered in the Genium Drafting Manual, Section 4.15 Screw Thread Design Considerations

For drafting personnel, the major purpose of this standard is to show how to place and draw the three methods of screw thread representation (simplified, schematic, and detailed) and also how to state thread requirements on engineering drawings. A few of the specifics covered in this standard are:

1. Showing and dimensioning the thread runout.
2. Drawing tapered threads, specifically making sure that they are tapered 3° from the axis.
3. Drawing thread inserts.
4. Dimensioning a thread relief.
5. Specifying a thread callout.
6. Specifying the thread series and class letter symbols.
7. Coating of threads.
8. Specifying pipe thread callouts.