Today while I was in Advanced Auto checking on prices for parts I had the guy look up the price on a mini spool for my 9". Well there were three options for 31 splines: Mini spool- steel, Mini Spool- steel 4-pinion, and Mini spool- Aluminum. I know the diferences between the steel and aluminum, but what does the 4-pinion mean? We called the dealer where they order there gears from and they didn't know what was meant by the 4-pinion. I am assuming that I just need the regular steel mini spool since it will be for a stock 9", but now I am just curious.