One thing to add, is that your instruction list should have the part number and description of every part in the kit. Therefore, as only an example (if you find or have found the parts list), look for something like this:
Part Number.........Type..........Quantity..........Description...............Size
000001...............Dowel..........1...............Lower Main Mast..........10mm x 300mm
000002...............Dowel..........1...............Upper Main Mast..........8mm x 150mm
This tells you that is the dowel RAW size to choose from parts stock, but not the FINAL shape. Go by the plans for the final shape using calipers or ruler.
So, get out all your Dowels and if you find a RAW size dowel that fits the measurements given in your parts list, then that is it. Then refer to the plans to make the shape.
I hope this helps.
Donnie