This bolster pair replaces the bolster on the AtlasO Trinity 5161 covered hopper with a bolster that allows you to mount a kadee #740 coupler and looks more realistic. To use it you will need to convert the existing Atlas O roller bearing trucks that came with the car with the appropriate bolster, or purchase the 100t Roller bearing trucks with Atlas style mount (not flush mount) from me. This can only be printed in FUD so it is quite brittle, if using the truck mount screw that came with the car you will need to either enlarge the hole in the truck mount pin, or tap it appropriately.