I’ve seen ad’s for this product, but wasn’t exactly sure what it was for since most of the text is in japanese.  It’s basically a rubber (that’s what GOMU means) for your shaft.  Get a tighter fit without the worry of your shaft getting loose.  I personally use O-Rings on my shafts and that seems to work, but I wouldn’t mind trying this product out.  Curious how much something like this costs once it get’s to the US Market, for comparison you can get o-rings for 2BA for about $0.12 each.