An el-cheapo brass BBQ brush has been the best file card I ever used, I have about 20 years on this one and it still works perfectly. I am a bow maker and use my 49 and 50 Nicholson all day long at times, they need constant brushing on some wood.
Someone said they gasped when they saw my file storage in another post, these are my use sometimes files, all are sharp. They may sit there with very slight contact with file next to them, but they never move, often for up to a year at a time if I am not building a gun. I am pretty sure they are not sawing back and forth against each other after I turn off the shop lights and go back to the house. I do have a ghost in my house so anything is possible, I have seen hundreds of things move on their own since my wife died, thankfully she hasn't ever rearraigned my shop in the dead of night, yet........
I do take better care of my bow making rasps that I use almost daily when I am building bows.