The headstock casting and its bearings went though several changes in the first years of production: on the earliest model (shown above) the headstock was decidedly flimsy with cast-in bracing beneath the bearings and the latter each pinched by a bolt that passed beneath it - the same arrangement can be seen in the pictures of a rare circa 1900 4-inch Drummond shown here. This design did not last long and by 1903/4 the headstock casting had been strengthened and the bearings changed to a type with a taper on their outside face and incorporating a screwed ring and serrated nut by which means they could be pulled into the headstock casting - and so closed down to set the running clearance on the 3/4" x 8 t.p.i. spindle. More pictures of this lathe here

1903/4 to circa 1905/6 Headstock - an expensive arrangement whereby the bearings were drawn into the headstock casting by large castellated nuts screwed onto the ends of the bearings themselves - a method that Drummond were to return to in 1921. 

1905/6 to 1912 headstock  - a cheaper design with the bearing drawn into the headstock by two screws passing through the casting and pulling on a large washer. Note the wide, rounded pulley on the top speed position - the only variant so far discovered to have such a feature.

1912 to 1921 The same design of bearing assembly as above, but with the headstock braced by an overhead bar in an attempt to reduce "chatter". Further details of this lathe and its headstock can be seen here.

The much stronger M Type headstock as used from 1921 until the late 1940s with improved draw-in spindle bearings, a quick-release bull wheel mechanism and a 1" x 12 t.p.i. nose thread backed by a 11/8" register designed to improve the rigidity of screwed attachments. The two cast-iron covers normally fitted over the backgears have been removed for clarity.

1921 to late 1940s M Type headstock with the an extra changewheel stud mounted in the front clevis - an arrangement that allowed left-hand threads to be generated.

The end of the spindle carried a simple screw-on sleeve to set the end float (the locking screw had a small copper washer beneath it to protect the thread) and another push-on sleeve, retained by a grub screw engaging against a small flat on the shaft, that carried a stud and hole to mate with the first gear in the changewheel train. The spindle end of the shaft can be seen here.