I'm confused ...

...
The end looks like 1.25" size, but there's no locking screw on it? ... I'm confused how I need to do the conversion from webcam 1.25" to this? ...
(I wish vendors would include more photo's of accessories, it's sometimes hard to tell what's going on with them like this..)
(hmm, tried submitting an enquiry to them though the email form (seems the only email way, and got an error.. bugger..)
Thanks