Good luck fellows on finding the head screws that you need for your older model OS Max .35 engines ..... the head screw (backplate screw is exact same size) that you need is indeed exactly 10 mm in length (measurment does not include head) and is 3 mm in diameter, but unfortunately with a .6 mm pitch. Like I say fellows, GOOD LUCK ..... you are going to need it! If anyone finds a source for 3mm x .6mm bolts please give me a clue, will you? Thanks Much!

Donald Garry