I had an arm rest that was very similar to this and it broke so I made my own version of it. Sooner or later ill add a top that has fabric but until the hard plastic annoys me I'm good with it how it is.

let me know what you end up using it for.

BOM:

Printed Parts:

• Print one of each part.

Non Printed Parts:

• 2 x Zip Ties
  • the ones i used are 5mmwide
• Squares
  • 4 x m4x20
    • m4x25 should work also but no longer than 25.
• Crank
  • 1 x m3x6 (or m3x8) for the crank
• Locking Square
  • 2 x m4x16
  • 2 x m4 nuts
  • 2 x springs

    • 6mmx10mm ( 1/4th x 13/32 )

      *I also used one that is about 7mmx12mm and worked fine.