Taking the key way measurement in SolidWorks draw


Dimension; Condition control.
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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. -
Step 2:
Change Centre to Max for the full width overall.
Done.