Smart Fasteners does not automatically add nuts or washers to fasteners. You add them in the Smart Fasteners PropertyManager. Each Group of fasteners has an associated Top Stack (washers added under the head of the fastener) and Bottom Stack (washers and nuts added to the end of the fastener).
See Toolbox Help:
Toolbox - Smart Fasteners to select or clear these options:
- Change fastener length to ensure
minimum thread engagement.
- Change stack components when
fastener size is changed.