fia0001 's Japan Review

I have no complaints at all about its performance as an o-ring.
It does not loosen or break. (Especially for fit shafts)

I was looking for a thin o-ring because I didn't like the way it felt and looked on my fingers when I put it on.

As a result, it is by far the thinnest, so my request is perfectly met, but I have to give it -1 for the balance of price/content.
That said, I highly recommend it.

For those who use fit shafts, which tend to loosen easily, but other o-rings stick out! I would definitely recommend it to those who use fit shafts and tend to loosen easily, but other o-rings stick out!

I use "Monster's barrel" and "fit's slim No. 8", but they are not compatible with each other or something. And when it is loose, the threaded part may be under extra strain, or it may break off frequently. I tried to use a foreign-made o-ring for a while, but the diameter was too thick and it protruded from between the barrel and the shaft, creating an unnecessary gap between the barrel and the shaft.

This product solved that problem.
As expected of Cosmo, the company behind the fit. It doesn't stick out and doesn't loosen even though it is thin. Thanks to this product, the shaft has not broken so far. If I keep using it, I'm sure it will eventually fall off badly and break, but that's just bad luck, lol.

One drawback is the price.
While other foreign-made o-rings and even domestic o-rings cost about 200~300 yen for about 20 pieces, this one costs 400 yen for 12 pieces. It is quite expensive. If the stress of shaft loosening is relieved and the shaft lasts longer, I think the original cost is enough.

For this reason, we deducted one star for cost performance and gave it 4 stars.

As others have mentioned, this O-ring is thinner than the competitor's product, so it does not stick out of the gap between the barrel and the O-ring.
When I install the other company's product on the shaft I normally use, it definitely sticks out and bothers me when I throw. This one does not, so there is zero stress.
I thought it would break easily, but it doesn't, so it is very useful.
I would have given it 5 stars if the price was a little lower...
Or 1.5x more...

I recommend this to anyone who is frustrated when slowing down due to a loose shaft.
This will relieve your stress!!!

It prevents the shaft from loosening, thus reducing stress.

The shaft hardly loosens at all.
I no longer have to stress about re-tightening the shaft every time I throw.
I would like to repeat this when I run out.