The four ball bearings are close together, to begin with. (loose to move within the tool). The round tube it slipped on the tool.
I then added another ball just ahead of the screw (inside).-- When advancing the screw it pushes the inside ball --forcing the balls (seen in the picture) to spread out to form the tube.
The first pic. shows the balls as extended.
The third pic shows the balls retracted to remove the tool from the tube.
BTW making ones own headers to go where they like them to go is a real challenge.--I enjoyed learning on my path.
The cut, fit, weld, finish, etc. was the fun/reward part for me.
Just a reminder for folks with a long-term project. (like me)--When It's done that fun part of building it is over. Enjoy the milestones of progress.
Making tools is a part of the hobby of fixing stuff.