A fold in which the orthogonal thickness of the folded strata is greater in the hinge than in the limbs, but the distance between any two folded surfaces is constant when measured parallel to the axial surface. Thus, if the shape of one bed is that of a sine curve, all the beds show the same shape. Similar folds show thinning on the limbs and thickening at the axes. Compare: parallel fold; supratenuous fold.