Currently the Line Width label shows 0.5mm increments, which is much to coarse for a typical formal line drawing. For good appearance only very few Line Widths should be mixed; similar to a good document, where a plethora of fonts should not be combined. This can be avoided by having only a few well chosen named settings: Suggested good Named Line Width settings: thin - 0.25mm - auxilary lines, hatchings, etc. normal - 0.35mm - 1pt - connecting lines, details fat - 0.5mm - Outlines, Symbols, Handwriting, etc. ultrafat - 0.7mm - simple outline sketches with little detail settable and selectable with pen-width selector label. The above would enforce good drawing practice and ease good looking formal drawing. They are spaced by a factor of approx. 1.4 (sqrt 2), so that the drawings almost always look well under almost any scale. Usually only 3 of the above would be used, a thinner set for detailed drawings, the thicker set for rough sketches with only a few lines and little detail.
Set as enhancement. Best regards. JBF
Added UX-advise mailing-list as CC Best regards. JBF
UX: one for you :-) Component -> ux-advise Status -> NEW
The steps are in 0.5mm, 0.1cm, 0.02in, 0.1pc, or 1pt depending on the setting under tools > options > (Writer) > Measurement unit. The control is a numerical stepper allowing to enter a value directly and to increase or decrease it by a fix value. If this value is too small you need to click too often for large changes. Your proposal is to reduce the freedom in favor of a dropdown with fix values. This will not work. The sidebar provides access to line thickness similarly to what you have in mind but in points. I believe that's better than using names since people needs to adopt to the actual values. Closing this issue as WONTFIX.