DNOSD240 - has a .15mm center hole in the nozzle pintle
DNOSD240/ - has a .20mm center hole in the nozzle pintle

The 240/ is a later design, starting in November of 1981. The design change to the larger center hole was presumably to quiet down the diesel knock a bit. Having said that, a set of brand new 240's is quieter than a set of 240/ with 200K on them.