In an engineering drawing, which letters written on the dimension indicates that it is extra information and NOT really required?

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RRB ALP Fitter 23 Jan 2019 Official Paper (Shift 2).

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Answer 1

Explanation:

REF:

In a technical drawing, a dimension or note is given only for reference and therefore is not intended to be used as a part acceptance criterion (although it may be used as an aid to production or inspection).
Parenthesis ( value ) denotes the same thing and were standardized by ASME (American Society of Mechanical Engineers).
When a dimension is defined in one view but also mentioned again in another view, it will be given as a reference in the second case.
This rule prevents the mistake of defining it in two different ways accidentally; the main (non-reference) mention is the only one that counts as a feature definition and thus as a part acceptance criterion.
In an engineering drawing, "REF" letters written on the dimension indicate that it is extra information and not really required.

EXT:

It is used for extension lines.
Extension lines usually connect dimension lines to different features on parts and images on the page.
They are drawn perpendicularly when connecting dimension lines.
For example, an extension line will reach beyond a complex object to connect with a dimension line that may give a specific height or distance.
When drawing an extension line, you should leave a 1/16-inch gap between the outline of an object and the beginning of an extension line.
Extension lines will extend another 1/8-inch beyond the outermost dimension line.