The Flat Free Tires by Tie Down Safety feature polyurethane, a solid substance that never requires air and is not vulnerable to leaks or punctures. This replacement wheel fits the Penetrator X3 or can be purchased separately and added to your own material carts. Every accessory or component product found at Tie Down is made by industry leaders. For over 50 years, Tie Down has established strong relationships with fellow manufacturers within multiple industries. Tie Down Safety maintains high standards and quality control through quality raw materials and components made in the USA.