These Countersunk bolts are to replace the standard ones which are removed when taking the engine out of the Discovery. The standard ones won't fit due to the bolt head protruding the Flywheel housing and are also too long.  Failure to fit these bolts will cause oil leaks. The flywheel housing gasket & rear crank seal doesn't form a good seal and therefore leaks from these due to the engine and flywheel housing flexing. The flywheel housing is only secured at the top and not all the way round. Using these bolts will also secure the ladder frame. These bolts need to be fitted before the engine is fitted into the vehicle

Note, These bolts are not for securing the gearbox to the engine