It is an AUD. Tat is an Under Drive model A.
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First the leadscrew must be turning which you will check while turning the chuck by hand. Then the chromed lever in the middle of the saddle must be in the middle position. Then the black handle on the right will be able to engage the half nuts (up) to enable threading – check still only under hand power. Then release that lever (down). There is an interlock between it and the chromed lever. The clutch does not affect this.
Move the chrome lever up to select feed. You may need to jiggle it a bit to release the interlock. Now turning the chuck will cause the clutch star wheel to rotate.
The clutch works by turning clockwise to pull a rod towards you that engages the friction clutch. Test still under hand power. There is a bit of slack to take up but eventually the big handwheel will rotate. To release the clutch rotate anticlockwise maybe a couple of turns but you also often need to push it in if it is sticky. The clutch is NOT meant to be done up rock solid so when under power holding the big handwheel should cause it to slip. Also you do NOT run the saddle up to the stop under power or it will move the stop. Use the handwheel to slow it down just before contact and gently control the last mm.
Don't forget the apron needs oil which has probably leaked out. If you do strip the apron there are two traps. The clutch central screw is a reverse thread. The grubscrew on the right side of the apron that should release the black lever has a second grubscrew deep down the hole.
Read all the Boxford threads on the forum. Th above advice and more has been repeated many times.