O-ring
From bildr
O-rings are used to create seals for Waterproofing Electronics etc. Parker also makes a calculator program that will let you pick the right o-ring and tell you how big to make the groove for it. A software screen shot is shown below listing design considerations for an example face seal(used for example to add a window to a waterproof housing so you can see a computer screen under it). Some of the key variables for this kind of seal are the gland depth, groove width, and diameter of the circle made by the outermost edge of the groove pattern(Groove OD/outer diameter). The material that you use for the o-ring is also going to be important if you're using extreme temperature ranges but the Parker software helps in material selection by allowing you to specify a temperature range and selecting the best material for you.
Software note :- You need to make sure to use a 32-bit version of windows or run it under the windows XP mode virtual PC If you're using something like 64-bit windows 7 or try their web version of the application. (The web version didn't work for this user).