This might seem like the most obscure thing I could ever choose to write about but seeing as I get asked it most days, here goes.
The most important thing to think about is thread diameter. Most spokes have 2.0mm threads, but DT Super Comps and some versions of Revolution and Comp spokes have 1.8mm threads. They are not interchangeable.
Then you have a choice of material. Spoke nipples generally come in either brass or aluminium and which you choose depends on your priority for the wheels you’re building. Brass nipples are tough, easy to build (as they will turn easily in the rim and not tend to bind to the spoke) and are easy to true at a later date as they don’t corrode onto the spoke very easily. They weigh exactly 1 gram each.
Aluminium nipples on the other hand have a reputation for being weak and easily corroded which can make the wheel hard to true at a later date, but these drawbacks are usually overstated; as long as good quality nipples are lubricated correctly when the wheel is built, and you use a top quality spoke key, they should be OK for several years. On heavily used wheels aluminium nipples may become brittle and prone to damage after about 3 years, meaning they break when being adjusted. At this point we can rebuild them with new nipples.
On the plus side, aluminium nipples weigh less than 1/3 of a gram each which can save 45g of fast-rotating weight in a pair of wheels. Even better, they come in a wide choice of colours.
Choice of material largely comes down to what you’re using the wheels for. If it’s racing or general XC riding on a lightweight rim then aluminium nipples is usually the best choice, as saving weight at the outside of the rim makes a big difference. If you are using a heavy rim (over 450g or so) you may as well go with the brass spoke nipples for longevity. Wheels which take a lot of abuse (ie, for downhill, jumps etc) certainly should be built with brass nipples; apart from anything, it will be easier to achieve the higher spoke tension such wheels demand.
Road wheels ridden in the winter on salty/gritted roads should certainly be built with brass spoke nipples; nothing corrodes aluminium ones faster than being left sitting in salty water. The water gets into the gap between spoke and nipples so can sit there for some time. It’s easily washed off, and we do recommend washing your bike (especially your wheels!) after every ride when the gritters have been out. Even if you just tip a bucket of warm water over it, it will make a big difference to preventing corrosion. We have learned this the hard way.
