O-Ring, EP, (50 pk). This O-Ring is primarily used for the ABI Amidite Clip Cap Seal. The original O-ring is made of Kalrez and we also carry that one under a different part number. The Kalrez O-Ring is rather expensive. EP is very compatible with Acetonitrile which is the solvent used to dissolve the amidites. We have used EP O-rings for amidite cap seals for 10 years with no problems and therefore confidently recommend the use of EP for this application.