A castor assembly structured for use in combination with or independently of a dolly or other support platform including a one piece base comprising a housing and a head integrally connected to the housing and extending radially outward from one end thereof. The housing includes an open interior and a open end structured to movably retain a surface engaging roller ball therein. A retaining portion may be formed on said base in cooperative relation with said head so as to secure a support platform to the base when in a first operative position. A second operative position comprises said head disposed in engagable and at least partially supporting relation to an object while the base is not secured to or used in combination with a dolly or other support platform.