Only to just have the blue ring visible. If you repack the bearings and get everything full you will probably never need to add any. Too many times have seen people pump way to much in too fast and damage the rear seals, but if you go slow and just pump until the end just pops out to where you can see the ring it will not hurt anything. I probably have close to 70K miles or more on my trailer in 13 years and the only problems I have had were from my own stupid mistake of replacing a bearing with a made in China one I had on hand as a spare instead of going to get another one that was made in the USA, and it bit me 3 months down the road when the roller bearing literally fell apart inside the hub.
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