FlexBollard has an impact resistant carbon steel torsion spring that provides 360° of flexibility allowing for a full range of movement. The square steel base measures 9" x 9". FlexBollard XL are very heavy duty flexible bollards that feature a galvanized steel base measuring 8" x 8" and 3/8" in thickness. There is also an upper post stabilizer with concealed 5/16" thick steel spring that offers long-term weatherability, while keeping the unit firmly anchored to the ground.