What is the filter size of the fixed 30xIS Canon Zoom Lens found on the PowerShot SX55IS?
Confirmed. The Canon Powershot SX500 IS doesn't have filter threads.
However this adapter has a few good reviews on amazon.com: http://www.amazon.com/Lens-Filter-Adapter-Canon-SX500/dp/B00A9HJ50U
Rather than using threads, it relies on friction fit to the concentric ridges inside the end of the lens.
This adapter uses 52mm filters, BTW.
Based on the image below there doesn't seem to be any filter threads on the end of the lens barrel.