The casting that fits onto the top of the bed. The term saddle is a self-explanatory, that is it slides along it is known, almost universally, as the “Saddle”
The vertical, often flat and rectangular “plate” fastened to the front of the “Saddle” is known as the “Apron”. It carries a selection of gears and controls that allow the carriage to be driven (by hand or power) up and down the bed. The mechanism inside can also engage the screwcutting feed and various powered tool feeds, should they be fitted. The leadscrew, and sometimes a power shaft as well, are often arranged to pass through the apron and provide it with a drive for the various functions.
All screw-cutting lathes have what is commonly-called a “half-nut” lever that closes down one and sometimes two halves of a split nut to grasp the leadscrew and provide a drive for screwcutting.
Apron design can be roughly divided into “single-wall” and “double-wall” types. The “single-wall” apron has just one thickness of metal and, protruding from it (and unsupported on their outer ends) are studs that carry gears. The “double-wall” apron is a much more robust structure, rather like a narrow, open-topped box with the gear-carrying studs fitted between the two walls – and hence rigidly supported at both ends. This type of construction produces a very stiff structure – and one that is far less likely to deflect under heavy-duty work; another advantage is that the closed base of the “box” can be used to house an oil reservoir the lubricant ion which is either splashed around or, preferably, pumped to supply the spindles, gears and even, on some lathes, the sliding surfaces of the bed and cross slide as well.