Luigi Wilkes Booth

11.5mm seems like a really oddball length. 12mm is the closest common length, and 0.5mm (.020") isn’t much. Have you already confirmed that a 12mm long screw won’t work? If so, grinding the tip down slightly with a rotary tool or bench grinder may be your best bet. If you can, thread a nut onto the screw before you grind it down. That way any threads that are messed up by the grinding will be restored when you take the nut off.