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 If you are short on cash, you can use a mini-spool, which you can see here. A mini-spool uses a stock diff case to hold the ring gear. It usually costs only $40 or so versus $120 for a full spool, but because it uses a stock diff case it also comes with about a 4-pound weight penalty versus a spool. That may not sound like much at first, but remember, we’re talking about rotating weight which must be spun up by the engine before it gets to the rear wheels.