Making bushings on a lathe - video

Making bushings on a lathe. By Swap lamp. 13:07 video:

https://www.youtube.com/watch?v=7dnhZFaS3y4

Wait so in the end of that video when he tightens the bushing in the arm what is transferring that hoop tension through the bushing to cause the tool post to lock into its rotational orientation?
Without a slit in the bushing that seems improbable to me....