Extreme heavy-duty rear steel CV (constant velocity) driveshafts feature larger 6 mm stub axles to work specifically with the Extreme Heavy Duty Upgrade Kit. Designed for intense high-power applications, these shafts are built to withstand the brutal torque from the 540XL motor and the massive grip of huge Sledgehammer^® tires. A unique splined telescoping design delivers full-range articulation, so there is never a need to limit suspension travel. When installing rear steel CV driveshafts you must use the included 6x12x4 inner bearings. Rear steel CV driveshafts are for use with the 9080-series upgrade kit only and will not fit standard suspension parts.