How to use different featured image size for a custom post type?

Want to use a different featured image size for a custom post type and exclude it from main blog loop. And also want to display it on specific page.

What will be the fastest way to achieve this? With code mess up and plugins?

Prefer a code snippet solution, but main issue it should work out-of-box, as fast solution is a priority.

Thanks in advance.

This might help – Set featured image size for a custom post type,

Just add a new image size

add_image_size( 'companies_thumb', 120, 120, true);

Then in the post type template for companies you just call the thumb
you defined.

<?php the_post_thumbnail('companies_thumb'); ?>