It isn't exactly correct to say that the Atlas and Craftsman 6" countershaft assemblies are different. Over the years from 1937 to 1973, Atlas built three versions of the countershaft assembly. The 618 undoubtedly used all three. As did Sears. On the Sears side, the earliest version appears on the 101.07300 in 1938. This is the version that used the L9-20 Bracket (the part that bolts to the bench). The only parts list known for the 101.07300 is the one on Sears Parts Direct. The next version uses the L9-20A bracket and on the parts lists available only appears on all of the (undated) ones for the 101.07301, which first appeared in the catalogs in 1939 (catalog actually printed in late 1938). The earliest dated 618 parts list that we have dates from 1950 and lists the bracket as M6-20B. There is an undated earlier one with a photograph showing what must be the L9-20A but the parts list with it lists M6-20B. Atlas was rather bad about this sort of thing. However, the change to M6-20B on the 618 probably happened in 1939, judging by the photograph of the 6" in Atlas catalog No. 39. The next older available catalog shows the L9-20A bracket.
The 101.07301, which was made up until sometime in 1957, apparently continued to use the L9-20A until the end. The 101.21400, which replaced the 101.07301 in late 1957 or early 1958, is the same as the 618 except for badge, and used the M6-20B. The photo of the L9-20 on Sears Parts Direct is just a black blob and the only photo I know of of the 101.07300 (in the 1938 Craftsman Power Tools catalog) hides most of the bracket. All that you can say is that the difference between L9-20 and L9-20A must have been minor, not major as with the M6-20B.
Robert D.
