The JR-TT105-BK kit contains aluminum rear upper suspension arms designed for TAMIYA TT01 and TT01E models. They are supplied as aftermarket replacements for the stock plastic arms and are formed to match the original mounting points so they fit the common hinge pin locations and typical rear suspension geometry used on these cars.
For chassis setup the aluminum arms provide reduced flex at the rear mounting points, which supports steadier alignment during tuning and testing. These parts are aimed at users who want predictable suspension adjustments and improved repeatability without replacing other major components.
Note on fitment: the components are made for the TT01 range and use the same chassis attachment locations; confirm fit on your specific TT01 or TT01E variant before final assembly, and keep or acquire any small fasteners required to complete installation.