The standard o-ring material is a high grade silicone rubber. This material will do fine for most applications, but if the equipment is subject to wetting with petroleum or cleaning solvents or if the fastener is removed and replaced frequently, another sealing material should be considered. For example, Fluorosilicone is ideal for sealing of equipment that is exposed to wetting with oil; Neoprene is good for frequent removal and reinstallation; Viton is ideal for oil exposure and frequent reuse.