I have attached the file I was working on.
I Drew this by sweeping a shape onto a rail and the line in the middle I have selected everything > Boolean > Merge. I do select all and trim when the Boolean merge does not work.

I m sure I am doing something wrong but I am not sure what

I created this same item different ways
from the line shape > offset to get the desired measurement and >extrude and the >flow to get the desired shape ( I had a hard time to flow the item to an exact length so I did the multiple times to be close enough ...is there a way to get the exact measurement for instance the shape to be flowed at is 516mm when I perform the flow it would be off my a few mm.

the other way was to create the shape and sweep around a rail which seemed a cleaner result.

If there is a better way (or steps ) to make this let me know


When I separated the items would be hollow and I cannot send it to print.

I just tried a new file with something simpler oval as a rail and sweep a shape around it then draw a line in the middle Boolean> Merge and it works fine but the file I am working on I cannot make it work :/

Thank you!