Those interested in replacing a missing thread chart on an older single-tumbler Heavy 10 may find the following helpful.
There are two variants of the 10L/10R single-tumbler box. They differ in the configuration of the tumbler arm and the idler gear bearing. What I surmise to be the older configuration, shown below, has a brass-plugged oil hole above the left side of the gear chart:
(The brass plugs are often missing. See
http://www.practicalmachinist.com/ubb/ultimatebb.php/topic/17/2640.html )
On the variant above the tumbler must be shifted all the way to the left (to the "4-128 TPI" column) so oil squirted in that hole can run down a brass tube and drip on the idler, idler shaft and pinion, by way of a little funnel in the tumbler casting. I've never seen instructions to this effect in print, and suspect many gearboxes (e.g, mine!) wore out simply because oil never reached the idler. Even if you do know the trick, the funnel is easily plugged with dirt and hard to inspect or clear.
The other version, which I guess is newer, has no front oil hole above the chart, but has an extra Gits oiler on the right side wall. The new oiler feeds a tube which dumps out over the "6-192 TPI" slot. In addition to more robust mechanical design (beefier tumbler, double-ended support for the idler shaft, and a needle bearing in the idler), SBL printed oiling instructions in the (previously blank) field at right of the 6-192 column. Here is the second variant:
The threading charts are identical except for this added oiling instruction, which is obviously incompatible with the older gearbox design.
Mike