Abstract: Apparatus for measuring non-cylindricity of surfaces. When measuring the non-cylindricity of bores, a plurality of pneumatic measuring transducers are mounted in radial holes in a circular cylindrical base element which is adapted to be introduced into the bore. Surrounding the outer ends of the nozzles of the measuring transducers are hollows which are connected to the atmosphere by means of passages extending within the body of the base element. The outer faces of the pneumatic nozzles serving as measuring transducers and the external cylindrical surface of the base element all lie on a common circular cylindrical surface. Successive measurements may be taken with the base element disposed in various axial and angular positions with respect to the bore. Means are provided for turning the base element either by hand or mechanically.