Taking the key way measurement in SolidWorks draw

Dimension; Condition control.

  1. Step 1:

    Dimension the Arc's of the slot. (It must be the arcs).
    Select the dimension, and click the leaders tab in the property manager - see the default is centres (for both conditions). If the Arcs were not selected; the arc conditions will not show.

  2. Step 2:

    Change Centre to Max for the full width overall.