How are they attached to the barrel?
There is a threaded adapter that fits on your barrel and on the filter. I have read that if you are shooting a .22, it will last you many thousands of rounds, but if you are shooting a higher powered handgun or rifle, the filter will last only a few. You then have to send the silencer back to the manufacturer and THEY will replace the filter for $25. I have read that is because once the oil filter is attached to the adapter, it is legally a part of the suppressor and the owner cannot modify it.