countersink head torx bit screws are common on flooring on cargo trailers and big dry van trailers. They are sometimes, but not always 1/4 - 20 thread. Many are an odd thread and are self tapping so they can be run in with a power driver. Too much power and the hole strips out and the screw won't tighten. This may be your situation. It may be possible to go to a larger size screw, you'll have to drill and tap the hole in the frame to accommodate the larger screw, probably 5/16-18 thread.