For this, different search methods can be used.
Example: The following part is searched.
With sufficient adequate table values (often very few are sufficient) you will find the part:
In the case of our example stating width, length, height and thread is sufficient, in order to get the desired part from an amount of one million parts at the third position in the result list.
25 160 54 M6
Of course, knowing an unique identifier such as product code or ERP number is ideal.
If you have a comparison part, regardless whether it's an own part or similar part from another catalog, the Geometric search (3D) is appropriate.
And even a single little sketch - not even particularly accurate - is sufficient to find the desired part.