This aluminum gear case from Strange allows the use of a 12 bolt ring and pinion and carrier in a 9" Ford housing. Why you may ask? There are a lot of very high 2 ratio 12 bolt gear sets available for use in Bonneville cars and the like. This case allows a car already equipped with a 9" to make use of these gear ratios. Or new vehicles being built can incorporate this case to make use of an ideal gear ratio but still have the versatility that the 9" rearend offers. NOTE: This case accepts carriers with 3.062" o.d. carrier bearings.