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Sold individually. These orings are used to stop First Contact Polymer flow on or under optic retaining rings (or retaining flanges if retained from backside). NOTE: Retaining rings sometimes do not fit sufficiently tight to the optic to disallow polymer from wicking under the ring. Once under a retaining ring the polymer will not pull out and will tear, leaving residue under the ring. Additionally, some retaining rings are plastic and are incompatible with the solvents in First Contact polymer so contact must be avoided.
These are chemical resistant orings that do not swell when in contact with the polymer. Do not use cheap Butyl or Buna orings, they will absorb solvents, swell and can break down leaving residue. Read our online Oring document with photos and text to explain oring use.
We have discovered that at least some mounted optics and filters are sold as a specific size, such as "2 inch diameter", but that is the optic size before mounting. The mount reduces the actual clear aperture so a 2" diameter oring may not necessarily fit an advertised 2 inch diameter optic. We recommend measuring the Inside Dimension (ID) of your retaining ring to select the correct oring size OD from the drop down menu.
NOTES: 1. If the orings are not flat when received and do not lay flat on your optic you can lay on a flat surface and apply mild heat with a heat gun and the orings will flatten. Allow to cool then apply to your optic! 2. The oring may trap a very thin layer of polymer underneath and leave polymer residue when peeled. This possible situation can be avoided by coating one side of the oring with polymer (or dipping), and once dry you can set in place and use per directions.
Shipping: If only ordering orings we can ship via USPS for less than than FedEx. Let us know if you prefer USPS and we will adjust the shipping cost to a flat rate $10.00 before charging your card. We will also send you a revised invoice showing the adjusted total cost. Applies to the Lower 48 United States only.
Why apply First Contact to your oring mating surface?
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