Orings can be used as a "dam" to avoid getting First Contact Polymer on your optic retaining ring. The retaining rings sometimes do not fit snug to the optic surface and the polymer, being a liquid, may possibly flow under the retaining ring and may not peel out, leaving polymer residue at the retaining ring edge. This also holds true for optics retained from the backside; the polymer can flow under the retaining lip. View our Oring Flow Control document to see photos and a description of how the process works.
Orings are an excellent choice for telescope eyepieces and filters, camera lenses, and protecting the secondary mount gasket on SCT corrector plates and primary mirror baffle tubes. Orings can be used for nearly any mounted optic!