To Add a User-Defined Size for an Existing Standard Part/Feature (AutoCAD Mechanical Toolset)

Click Content tabLibrary panelContent Manager. Find
In the Content Manager dialog box, in the Content panel, right-click the item to add the size to and click Edit. The Content Editor starts.
If the Family Table is not displayed
- Click Content Editor tab Manage panel Family Table. .
Locate the row that corresponds to the size nearest to the size you want to create.
Right-click the row header and select Add Row
Right-click the row header again and select Copy.
Right-click the row header of the row you added in step 5 and select Paste.
Both items are now identical with the exception of the disabled columns, which are protected by the system.
In the Size column for the newly added row, change the description to reflect the new size. For example in a screw the size can be expressed in the form of 1/4-20 - 5 1/2.
In the cell that controls the dimension you want change (for example, the nominal length of a screw), enter the new value.
Close the Content Editor.
Click Save when you are prompted to save the content.