Another addendum - some of the metric threads shown on the Atlas change gear type threading charts also required a special spacer (gear) that was smaller in diameter than the 20T gear (smallest double-keyed one that Atlas made) or regular spacer (same OD as the 20T gear). And another part that I forget the details of. The Atlas MOLO said to make the special spacer by turning down the OD of a 20T gear or standard spacer (probably because the spacers also have to be double-keyed). I don't mean to imply that the Atlas special parts might fit the Clausing but that it might take more than just additional stock gears.
Another thing that I'll mention is that an Atlas owner in South Africa (not the Atlas factory) figured out that he could get 1.0, 1.25 and 1.5 mm pitch without swapping out gears on the banjo by replacing the pair of 48T gears on the banjo that actually drive the QCGB with the 52/44T combo. The Atlas sysem has a 40T sliding gear than can be moved in or out to mesh with the 16/32T pivot gear on the tumbler. With the sliding gear OUT, it drove the 52T gear as an Idler, which in turn drove the gear box. And all of the gearbox settings from 8 tpi to 96 tpi still worked the same. With the sliding gear IN. it drove the 44T gear which turned the 52T gear as a compound gear. Then setting the gearbox to 60, 48 or 40 tpi gave 1.0, 1.25 or 1.5 mm. You lost 4 to 7.5 tpi capability. which aren't commonly used. Whether other gearbox selector settings would give other valid metric pitches or not, he didn't say. Those three pitches must have been all that he was interested in.
The Clausing QCGB equipped 100 or 4800 Series lathes use different pitch gears on the banjo and tumbler so the numbers above won't work (and 60 tpi isn't an option on the Clausing). But maybe someone figured out something similar.
