This is a replacement roller for a Gamut dual ring chain retention device for Mountain Bikes. Gamut no longer makes this part. Replacement 8X22X7 bearings (2 required) are available from TheBearingStore.com.
I have been using one of these printed in white plastic on my Specialized Carbon Stumpjumper Evo 29 for over a year now. It appears to be holding up better than the original part!