I had an old Celexon Beamer Canvas sitting in the garage for years, the plastic cap broke and I finally decided to design a 3D printed model part and fix the canvas. I've searched everywhere for a part like this, sadly Celexon doesn't sell replacement parts for their products, and I haven't found any other 3D designs on the internet. My design has a lot of flaws but is usable and it does the job.

PS. the canvas is for the version with springs , not the electric one.