The Unifoc 58 and Unifoc 76 helical mounts are used for focusing the enlarging lenses, which do not contain any internal focusing mechanism. The helical mounts offer a total focus range (Z-axis travel) of 25.7 mm and differ only by their rear mount. The Unifoc 58 has "male" T2 thread (M42x0.75). The Unifoc 76 has a "male" M58x0.75 thread. The Unifoc 76 is the best choice for cameras with long linear CCDs.