Ford 9" Racing Spool31 Spline AxlesLightweight: 6.05 lbs.2.891" & 3.062" Cases1.78" Journal SizeCNC Machined 4130 Alloy Steel Note:Made to fit Ford 9" stock differential housing without any modifications. Requires the use of spool bearings.The industry standard for dirt track racingWhen installing in a 2.891" housing use 873-D1586 or 836-29-0002-1 bearings (sold separately).When installing in a 3.062" housing use 873-D1588 or 836-29-0004-1 bearings (sold separately).