Mounting a Merlin hotend under a Bulldog lite extruder seems to be a simple job. Be it a manufacturing tolerance or whatever - the top part of the Merlin fits into its seat in the Bulldog, but it enjoys some freedom to move around even if the holding plate is tightly screwed to the Bulldog body. This ia undesriable. There remains a gap between the Merlin's 'groove mount' and the Bulldog's bottom - at least if the brass screw there is compltely turned in, as it is in the delivered extruder. I just turned that brass screw with the filament duct a bit (about a half turn, ydmv) out of the Bulldog's body to compensate the distance. When the groove mount is pressed up to it by the holding plate, the gap is closed now, Merlin has no chance to move any more. The screw is pressed to its thread so it should not rattle loose.