I followed this tutorial to getting featured images to show in the admin menu on posts. I wanted to be able to see what article had a featured image and what it looked like without having to actually edit the article.
The article worked, but I noticed that it didn't work on my custom post type. So I went looking for the filter that would make it work and found manage_edit-post_type_columns
I have a custom post type for "Events". The slug for this is "events". I figured from the codex that if I did this
add_filter('manage_events_custom_columns', 'ST4_columns_content', 10, 2);
It would work but it has not. I can see the column for the featured image in the admin menu but I do not see the image in the column next to the post.