Jorn, if you're using the U-shaped tool for the first time to remove the old tumbler it may take some fiddling to get the tumbler to release. Best to fabricate the U-shaped tool from the largest diameter wire that will fit in the tumbler slots. Like with most things, after you remove the tumbler once you will know the feel to release the keepers if you ever need to replace a tumbler in the future.

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Fred Hoelzle