I made this top rail mount for an eSun filament dryer box, to be used with a direct drive system on an Ender 3 Max. Printed at 25% triangular infill with normal PLA, it is more than strong enough to support the dryer box and a full 1kg roll of filament. NOTE - it is a press-fit, meaning it is a very snug fit. Because different brands of filament have higher/lower expansion properties, I highly recommend that your filament is dried down to around 10%, and it is best to print the small test piece to see how it fits. If it is too tight to slide firmly onto the rail, increase the inner and outer dimensions equally by a half mm until it is a snug fit that can be slid along the rail with some force. I added a LED mount to the underside. The small alignment washers go on the top under the bolts, to keep it square.