A generalised non-dimensional multi-parametric model for involute spur gear design is presented, considering manufacturability and geometrical compatibility, where the latter considers various modes of interference and accounts for the combined effects of the module, pressure angle, tooth addendum, dedendum, cutter tip radius, and the numbers of teeth of a pair of mating gears. The effect of the same parameters together with tooth thickness on the manufacturability of the individual gear teeth is also modelled in terms of pointing and undercutting. The full range of parameter values, including non-standard ones, is considered. The resulting combined model serves to provide a complete analytical overview of the multi-parametric design space and is suitable for the fast assessment of existing designs, for implicit or explicit (direct) gear design, for extracting design guidelines, and for design optimisation. The model can be used to identify and explore highly promising under-used subspaces of the parametric design space, which are currently of significant interest to i.e. the automotive and aerospace industries.@en