Something to consider as an alternative is having some lengths of PVC tubing to take up the slack at the top. An eBay seller shipped me a pen packed in a PVC tube once, and by nice coincidence, the tube closely matched the shaft diameter of my Paterson tanks, so I chopped it up into short spacers, and, voila, no more rising reels.
Originally Posted by Trevor Crone
I wind up using 600ml for 120 film anyhow because I use XTol 1:2 with two rolls on a reel with a minimum of 100ml stock per roll. I still have a couple of rolls with a thin edge where the reel rode up the shaft prior to my using PVC spacers.