Search with dynamic results A couple questions...

1) How do these dynamic searches work? A excellent example is found at McMaster Carr website

2) Is there any search plugin like that for Craft? I did not see any.
You don't really need a "search" plugin for that. Craft has a brilliant Query Builder so it can be done really easily. Furthermore there is the Element Api which provides a JSON endpoint. 

I suggest you to read the docs about Searching in Craft and about Queries in Templates.

If you wan't to search for entries containing these words, a specific length and a threadSize you could do

{% for entry in craft.entries.threadSize('and, &gt;0, &lt;80).length('and, &gt;10, &lt;100).search({
    query: 'socket head screws',
    subLeft: true,
    subRight: true                
}).limit(10).all() %}
    &lt;article&gt;
        &lt;h1&gt;&lt;a href="{{ entry.url }}"&gt;{{ entry.title }}&lt;/a&gt;&lt;/h1&gt;
        &lt;a href="{{ entry.url }}"&gt;Continue reading&lt;/a&gt;
    &lt;/article&gt;
{% endfor %}


That's basically it.

For advanced searches I would recommend to create a custom plugin. It's totally easy to search things in Craft so the need of a "default" plugins is not really high and it's faster to create a custom plugin than to find one that fits all your specific needs.