A mechanical separator for separating a fluid sample into first and second phases within a collection container is disclosed. The mechanical separator may have a separator body having a through-hole defined therein, with the through-hole adapted for allowing fluid to pass therethrough. The separator body includes a float, having a first density, and a ballast, having a second density greater than the first density. A portion of the float is connected to a portion of the ballast. Optionally, the float may include a first extended tab adjacent a first opening of the through-hole and a second extended tab adjacent the second opening of the through-hole. In certain configurations, the separator body also includes an extended tab band disposed about an outer surface of the float. The separator body may also include an engagement band circumferentially disposed about at least a portion of the separator body.