DIWdiver
Flashlight Enthusiast
Hmm... The recommended stretch is 1-5%, and this application would stretch a 0.989" o-ring onto a 1.000" diameter, so that's 1.1%. A little thin, but within range.
Squeeze should be around 30% for 'static' seals (parts don't move during use), and around 20% dynamic seals. The ID and OD of the light parts are 1.000 and 1.125, or radius of 0.500 and 0.5625. That's a difference of 0.0625, and the o-ring thickness is 0.070, so the squeeze is (0.070-0.0625)/0.070=0.0107. That's 10.7% squeeze. That's pretty thin.
What does the o-ring get pushed up against when pressure is applied? On my light, threads are cut right through into the o-ring area, so the o-ring is pushed up against the cut threads. That's not good at all. On the other hand even rather deep diving depths of 300 FSW are only around 5% of the pressure that the o-ring could handle in a properly designed system. Also the parts don't move when pressure is applied, so at low pressures there is likely to be little or no damage to the o-ring.
The next thicker ring in standard AS-568A sizes would be a -120. Stretch would be 1.3%, but since the thickness is 0.103", the squeeze would be 39%. That might make it difficult or impossible to close the light, could damage the o-ring during assembly, and it might degrade the lifetime of the o-ring (though replacing it once a year would be pretty reasonable).
Maybe you could find a metric size that would match better. Apple Rubber has two sizes that would fit the recommendations, but it might take a lot of money to get a few of them.
Bottom line: A light using the MAG-C parts and the stock -022 o-ring would probably be fine, but I wouldn't put a lot of trust in it. If I could close it with a -120 o-ring installed, I'd be happier. If I could get a metric or non-standard o-ring closer to the ideal 0.98" (24.9mm) ID and 0.0893" (2.27mm) thickness, I'd be much happier.
D
