Fasteners often include things like Screws, Bolts, Rivets, Nails etc. and as part of that would also include Washers, Nuts, Helicoils etc.

It is often beneficial to have Part files that represent your fasteners in an assembly so that the BOM is as accurate as possible, but there are many options for including these in your assemblies

SolidWorks Handles Fasteners in a variety of ways, the most integrated way being the utilization of the Toolbox

To utilize Toolbox, each computer must be configured in a specific manner to handle the Assembly identically, otherwise one PC will open one assembly one way while the next may open it completely differently

On small-scale usage of SolidWorks, it's not uncommon to create a Standard Parts Library for users within your company to utilize

This library would be a network-folder that everyone has access to which contains parts that are frequently-used and rarely-modified

McMaster-Carr contains nearly every fastener available but also has a downloadable version of that file that was generated using SolidWorks!

1. McMaster.com

2. Screws→Click through options

3. Select Part

4. Click Product Detail

5. Go to CAD→Select SolidWorks

6. Click Download

Often times instead of inserting an entire 3D model, you'll just want a part to represent the file

1. Insert New Part

2. Check-it-out

3. Check-it-out

You'll need to change the virtual part's properties so that it will display properly in the BOM, but it's now accounted for.  3D model information can always be added at a later time