For comparison wit the ZF.41 below, this ZF41/1, also coded “cxn” (Emil Busch A.-G., Optische Industrie, Rathenow), is a later type II sight. This model doesn’t use flat rollers anymore.
ZF41/1 coded “cxn” for the manufacturer Emil Busch A.-G., Optische Industrie in Rathenow. The “M” marking meaning remains unknown today.