The IEC 'Dynamics Carts' are the best in the business and they last many years. They have inboard wheels to avoid tangles, they are the strongest and are most rigid, they offer the least rolling friction and are safer than others. They are supplied as pairs and each cart has the full pin firing facility. A safety catch is included that allows the firing pin to be locked and unable to fire. This IEC invention greatly raises the safety level when using carts. Our carts have been sent overseas for absolutely exact visual copying, so look for the IEC hexagon logo and super free precision wheels on the underside before purchasing.