M6 are too big - there isn't enough plastic in the box to hold them. There are plenty of M5 versions on ebay. I drill the original holes out to 8mm before fitting them. If you're replacing the screws I'd go for something 5mm longer than the originals as the threads are recessed in to the D nuts slightly. The original screws will just catch, except where the HVAC sensor is - you definitely need a longer one there.
|