Flue cap question

[Syncop8r]

In order to clean a flue, all of the videos and other instructions I have seen so far say to remove a screw in order to take the cap off.
What if there is no screw?


Things may also be done differently here....?

 

[Cody]

Give 'er a twist.

 

[Sandhill Crane]

Yes, if it is double or triple wall, good chance it twist locks.