1. BASIC DIMENSIONING RULES

2. Dimension Terminology
Extension line
Arrowhead
Dimension number 59
Dimension line

3. Extension lines
Extension lines should extend 2 mm beyond the dimension line 40
Extension lines should be offset from the part by 2 mm

4. Dimension Spacing
The first row of dimensions will be 12 mm away from the part. 40 20
Any dimension beyond will be 8 mm apart.
That is a reference for a 4mm high text.
Generally speaking, dimension numbers should be centred between arrowheads.

5. Arrowheads and numbers
Should be 3 times longer than they are wide.
Always dimension the actual size of the object, not the scaled size.
For metric drawings, omit the use of the millimetre (mm) notation following the number, as millimetres are the default units.

6. Basic rules
Do not duplicate dimensions and avoid using unnecessary or superfluous dimensions.
Dimensions should be attached to the view that best shows the shape of the feature to be dimensioned.
All horizontal dimensions are read from the bottom edge of the paper and all vertical dimensions are read from the right-hand edge of the paper (aligned system). The number must be placed above the dimension line.

7. All horizontal dimensions are read from the bottom edge of the paper and all vertical dimensions are read from the right-hand edge of the paper (aligned system). The number must be placed above the dimension line. 40
110 40 50 70 70

8. Do NOT duplicate dimensions and avoid using unnecessary or superfluous dimensions. The same information should NOT be given in two different ways. The overall dimension should always be given. It should be placed outside of smaller dimensions and be the farthest dimension from the part.

9. NEVER cross a dimension line and an extension line.
The overall dimension should always be given. It should be placed outside of smaller dimensions and be the farthest dimension from the part.
NEVER cross a dimension line and an extension line. 16

10. Avoid placing any dimension on the part (inside the view) unless there is no other option.40 40
BAD PRACTICE
GOOD PRACTICE 16

11. A dimension should be attached to only one view (i. e
A dimension should be attached to only one view (i.e., extension lines should not connect two views). 40 40
BAD PRACTICE
GOOD PRACTICE 16

12. Avoid dimensioning to hidden features.
Dimensions should be attached to the view that best shows the shape of the feature to be dimensioned.
Avoid dimensioning to hidden features. 40 40
GOOD PRACTICE
BAD PRACTICE 16

13. Extension lines may cross each other and over other lines on the part, but dimension lines should never be crossed (if possible). 16

14. Never use a centre line or a line of the view as a dimension line,...
... Never draw a dimension line as a continuation of a line of a view ...
Don’t use a line of the part as a dimension line...
… but centre lines can be used as extension lines

15. Circles and arcs
Ø 25
In general, a circle and an arc greater than 180º is dimensioned by its diametre. An arc less than 180º is dimensioned by its radius.
The dimension lines must be placed at different angles.
No more than two concentric circumferences can be dimensioned in the circular view. The other ones will be dimensioned in the rectangular view. 45
Dimension cylinders in their rectangular view with a diametre symbol (Ø).
DON’T PLACE THE SYMBOL IN THE CIRCULAR VIEW. 65

16. When there is lack of space, the dimension number can be placed out of the arrowheads (to the right)
If it is not enough room, the arrowheads can be placed out of the extension lines, pointing inwards.
When there is no room for the arrowheads, they can be replaced by a point… 45
156 35 50