HD cylinders offer long life in harsh conditions and are NFPA interchangeable. They come in 5, 8, 10, and 12 in. bores and have a heavy-duty external rod bearing in rod end cap that is Teflon-impregnated and hard-coat anodized for smooth motion and rod rigidity and stability. Mead Fluid Dynamics Inc., (773) 685-6800, www.mead-usa.com