70 is formed of flat stock and is bent to embrace the inner end of framing shaft 38 in grooves 64 and 66 in normal positioning the ends of spring 70 are closely adjacent stop shoulder 68 in the assembled position the spring 70 resiliently embraces the inner end of the framing shaft within grooves 64 and 66 the inner end of advance shaft 54 has a plurality of detent flats 72 thereon when advance shaft 54 is in position within framing shaft 38 these detent flats lie under spring 70 it should be noted that both advance shaft 54 and the bore 56 in which it is positioned are tapered with the smaller end toward sprocket 22 this tapered construction aids in the assembly with spring 70 in place advance shaft 54 is thrust into its bore when the nose of detent flat 72 approaches spring 70 the nose is lower with respect to the spring because the tapered advance shaft 54 is not fully into its bore this permits the detent flat 72 to enter under spring 70 as the advance shaft 54 is fully engaged in position the tapered character of the shaft and its bore cause the detent flat 72 to slightly rise as it is moved in to prestress spring 70 now spring 70 urges advance shaft 54 into a particular angular position with respect to framing shaft 38 as dictated by the detent flats the number of detent flats 72 is related to the diameter of sprocket 22 and the distance required to advance film.