Turns a single Auto Dolly into a highly moveable engine/transmission dolly, "Gentle-V" design provides self-centering stability, Free up storage space in your garage or shop: Easily move engines aside, even under a workbench, Facilitates shop or garage orderliness and efficient floor cleaning, Works on Standard or Heavy Duty Auto Dolly (match your caster size). 12" or 16" Dolly recommended.