There are two basic configurations for o-ringThe rubber ring that seals underwater camera equipment. seals; the `Piston' seal, and the `Gasket', or compression seal. In the former, one part of the assembly slides into the other, while in the latter, the O-ring is squashed by a lid. The back doors of Nikonos and Motormarine cameras have piston seals. The back doors of most SLR housings have gasket seals. The O-ring grease is not a sealant; it is a lubricant that enables piston seals to be assembled without damage. Consequently, gasket seals do not need grease, although a light coating may help to preserve the rubber and may assist in cleaning. If grease is required, the type used is very important. In the past, camera O-rings were nearly always made from Nitrile-Butadiene Rubber (NBR), usually black, and the appropriate lubricant is either petroleum gel (i.e., Vaseline, or Nikonos Grease), or preferably Silicone grease (e.g., Molycote 111). Nowadays, Silicone O-rings are common. These are often colored, and can be recognized by their textural similarity to silicone diving masks. Petroleum gel can be used on some silicones, but silicone grease will cause the material to swell and fail in service. The correct lubricant for silicone rubber is fluorosilicone grease (e.g., Molycote FS1292).

It is also important to distinguish between user seals (like the back door and the battery lid) and control shaft seals. User seals and static seals need only to be greased before assembly, but control shafts need to be packed with lubricant. If you simply grease a control shaft seal, it will soon dry out and fail through abrasion.