The OS expanded rear differential cover is made of cast aluminum and is designed to aid in additional fluid capacity. 

Stock capacity is 0.6L of differential fluid and has been found to be inadequate for heavy track abuse which leads to frequent fluid changes. Effectively doubling the fluid capacity has proven to extend that fluid change interval and will aid in improving the long-term health of the differential internals as well as the associated bearings and seals. 

The cover is dimensionally identical to the OEM unit for precise fitment and retainment of the OEM side bearing tolerance. It also has additional ports to aid installation of a differential cooler as well as a temperature sensor for data acquisition.

-Increases the total fluid capacity to 1.2L compared to the OEM cover of 0.6L
-Includes (2) 3/8-NPT port plugs 
-Includes (1) 1/8-NPT port plugs
-Reuses factory drain/fill bolts and upper breather assembly from OEM cover
-Factory fasteners are reused.
-Direct install for OS Giken LSDs. No additional clearance needed to the cover for install.