Hendey Screwcutting gearboxes were available in both English and Metric types - with conversion gears to convert each to the other type of screwcutting.
If the external threading plates are lost the gearboxes can be distinguished by the line of the selector holes: the English box slopes from right to left, the Metric box from left to right.
Part-sectioned drawings of the gearbox can be seen here.

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