The Invincible 900 Series adopts the best features of our series 450 and 500. While rated at lower pressures, it has higher movement capabilities, a full vacuum rating and lower spring rates. All joints are hand built by our skilled craftsmen. The 1/4” minimum thickness solid elastomer tube is continuous with the flange face. Multiple plies of rubber impregnated high strength polyester or nylon tire cord form the first pressure reinforcement over the tube. Arch swell in response to pressure and arch migration are virtually eliminated by crisscrossed layers of reinforcement that pass over the arch and around steel rings embedded on both sides at the base of the arch.