You may find the nipples don't twist on the threads properly, and instead just twist the spokes instead - this can make them break quite easily, especially with older ones. It's a really good idea to lubricate that whole area.
Put some oil on the spoke just where it enters the nipple and also just where the nipple enters the rim, then spin the wheel fast for a minute or two. If the tyre's off, dab some oil onto each nipple from the inside of the rim too.
Spoke nipple sizes differ. Take the wheel to your LBS and get them to tell you which one you'll need.
For an old wheel, I recommend getting a spoke key that grips all four sides of the nipple to avoid rounding them off - see the discussion here: http://roadcyclinguk.com/tech/maintenance/winter-wheelbuild-part-one.html
You may find the nipples don't twist on the threads properly, and instead just twist the spokes instead - this can make them break quite easily, especially with older ones. It's a really good idea to lubricate that whole area.
Put some oil on the spoke just where it enters the nipple and also just where the nipple enters the rim, then spin the wheel fast for a minute or two. If the tyre's off, dab some oil onto each nipple from the inside of the rim too.
Good luck.
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