The HR is a family of straight-3 12-valve and straight-4 16-valve automobile petrol-only engines with continuously variable valve timing, involving development by Nissan and/or Renault, and also Mercedes-Benz in the case of the H5Ht/M282. The designation of H engine is used by Renault, and M28x by Mercedes-Benz, to classify the family. There are three basic specifications of engine involving variations in engine architecture, or all-new architecture, with 72.2 mm (2.84 in), 75.5 mm (2.97 in) and 78 mm (3.07 in) bore diameter.