Abstract: The shaped block in the path of the fluid from the nozzle of a high pressure fluid jet to be located below the material to be cut or slit by a jet including, preferably, a curvo-linear passage or bore through the block having an entry port aligned with the nozzle for receiving and directing the flow of fluid from the jet after it has slit the material and preventing the fluid from returning to or splashing upon the material after it has entered the passage and a replaceable slug for insertion into the block in the area where the high pressure fluid impinges as it enters the passage.