Interchangeable Speedometer Pinion Gear
compliments of Nissanman
There is a caveat to this just so everyone knows - you can't just change pinions from say 16/17 to 18,19,20 - you ALSO have to change the carrier because of the larger offset, OR you have to realign the carrier.
Also, it is not just a matter of matching pinions to transmission - you also have to work out which is needed based upon wheel dimensions.
Carrier/pinion sets are available from Nissan P/N 32702-58SXX - where xx is the number of teeth.
Ross (Sports Imports) already has a pretty comprehensive list in the Wiki.