Two versions of the Boxford power-feed apron were made: the first type, an exact copy of that fitted to the American 9-inch South Bend lathe, was fitted with a metal screw-in knob to engage the drive. The second type was similar but of more complex construction, this being produced as a safety improvement - its black plastic engagement knob, unlike the metal type, remaining stationary as the drive worked.
The early apron is shown below (with data about dismantling and rebuilding this unit found here) and the second type, with pictures of a dismantled unit and the various parts, on Page 2 here. 
series of photographs showing the Boxford and South Bend power-feed apron as fitted to the model A and B machines.
In the centre of the apron is a 3-position quadrant lever: with the lever in the middle the drive is in neutral; lifting the lever up into the top position gives a sliding feed along the bed; putting the lever in the lowest position gives power cross feed. With the tumble-reverse lever set to give a  feed along the bed towards the chuck, if the power cross feed position is then selected, the drive will be outwards towards the operator. To make the cross slide move inwards and take a normal cut across a job, the tumble reverse lever needs to be  moved to its other position.
Putting aside condition and accessories, what, one might ask, is the most important consideration about its specification that most be born in mind when choosing a Boxford lathe? The answer is - the apron. It is sometimes not appreciated that lathes with power-feed aprons - the Models A, AUD, B, BUD and VSL and B - not only benefited from power cross feed but also a range of slower longitudinal feeds than the Models C and CUD, the reduction through the apron's worm-and-wheel gearings meaning that the feed rate was reduced by a factor of 0.3. In addition, because the power-feed drive was taken from a key running in the slotted leadscrew, the thread in the latter was needed only for screwcutting, so preserving its accuracy and saving wear on the expensive clasp nuts. As the Model C lathes, with their plain apron, need to have the leadscrew clasp nuts engaged for a sliding feed, this causes them to be worn well before any other part of the lathe. As the nuts are only occasionally available - and expensive - any version of the Models C is, unless in really sound condition, best avoided. The power-feed apron on the Boxford was identical to that used on the South Bend "9-inch", with the drive taken through what was, in effect a cone clutch wound into engagement by a star-shaped knob on apron's front face. If this clutch is allowed to slip (by regularly running the carriage up against a bed stop for example) the mating surfaces of the cone will eventually become polished and, no matter how tightly the knob is screwed in, will slip badly. The solution is to strip the clutch and roughen all the friction surfaces - the spilt cones and their seating - with fine emery cloth; once done this will allow the drive to deep cuts with only the lightest of pressure on the control wheel. A useful thing to know when dismantling the apron is that the screw in the centre of the clutch wheel has a left-hand thread - it's a 3/16" BSF (British Standard Fine). However, it's now far easier and cheaper to source a 2BA and there is less than ½ a turn difference in the screw length required between them (just Google 2BA (British Association) nuts, bolts and studs.
On late machines, for both safety and ease of use, the clutch wheel was prevented from rotating by the use of needle-roller thrust bearings fitted to both front and back of the engagement shaft with a peg added to its end that located into a hole in the cover plate. These late-model aprons can be instantly recognised by their black plastic clutch-control wheel, the earlier type being in cast-iron. Unfortunately, the clasp nuts, though of a straightforward design, do tend to fill up with swarf and dirt and so, to protect the leadscrew, it's worth removing the apron from time to time and cleaning them out carefully. In the case of the Model C, where the clasp nuts are in constant use (taking the place of the power-feed mechanism) it may be necessary to pick embedded material from the thread roots with a sharp-pointed tool. An adjustable friction device - a spring, ball bearing and socket-headed Allen screw - located underneath the apron towards its tailstock end helped to hold the clasp nuts in both their open and closed positions.
All types of Boxford apron are notorious for building up a messy collection of swarf, dirt and grease - hence, if your lathe is well-used, it's a good idea to remove the apron once a year, strip it down and thoroughly clean and lubricate all the parts..