This is a true story. I live in the West, and I usually know the postal delivery person, quite well. And as advertisements for auto dealers they'll send out an ad to everyone with a thin key, claiming you've won a free car, either if the key fits, or you won but all you have to do is give an email address so they can spam you and you won, but only a Wifi speaker. Well on a windy day a bunch of those ads blew away. So I went and collected them. They were destroyed by landing in gutter water. So I got a bunch, but I has already known about those keys and cracked the code a few years before. I loose keys all the time. Any way, on cb400f, those fake keys, all you gotta do or any key that goes into the key hole can be made in seconds to open and lock and function perfectly, and often even being able to lock the steering., with a sharp file or knife starting where the the peaks and valleys begin halfwaydown from the the handle and going towards the tip, start aggressive filing or shearing, shaving tapering to the tip, it can get pretty thin. But if you remember only slightly how yours was shaped, you can short cut the process, just tapering at the tip, and you'll have either spares, or the master set., the seats, most of the time will open with a screw driver or another key that will side in. I always have a spare or 2, under the seat. It's a small town. Oh the beauty of the car dealership keys, is they are ambidextrous. The groves are very shallow and the same on each side. Watch for those keys in the mail.