A typical parallel or concentric fold with subclass 1B geometry, orthogonal thickness reamining constant along individual folded layers.
Folds which maintain the orthogonal thickness at the cost of form of folded surfaces. Typical subclass 1B folds of Ramsay. See concentic folds. Such folds typically for by flexural slip or interlayer slip, the examples being chevron folds and conjugate kink bands.