A sub-species of the ever-popular 4L, the G. Boley Model 4L.E. was manufactured from the late 1930s into the 1970s and displayed numerous improvements over earlier versions. While an early 1950s lathe is shown on this page, an even later one, catalogued as the "New Streamlined Size 4" and offered as the Models Types 4E and 4H, was made the early 1960s onwards. In addition, other versions come to light, some yet to be found in the sales literature and so possibly short production runs for a customer's particular requirement.
On the version shown below, while the top slide was given a greater travel, and the tailstock provided with a longer and more robust casting, the most significant alterations were to the bed and saddle - with the latter being thicker over its centre section and with very long arms added to its left-hand side. In conjunction with the alterations to the carriage, the bed was modified so that the ways ran on past the front and back of the headstock to give greatly improved support for the cutting tool as it neared the spindle nose. That part of the bed abutting the headstock was braced by the addition of a large triangulated section on the underside, the headstock given a more robust spindle, running in larger diameter bearing, and the backgears increased in size to cope with heavier work. The 3-step pulley was reversed, to bring the largest diameter to the left, and the arrangement for engaging backgear - previously rather fiddly - redesigned for simpler and more certain operation. The 4L illustrated immediately below is fitted to an underdrive stand, the cost of which (if other Boley price lists are a safe guide) would have nearly doubled that of the basic machine.
Although early models were mounted on traditional-for-the-time stands - a cast-iron chip tray supported on simple standards to which was affixed, and completely exposed, the motor-drive system - by the 1940s some improvements had been made with a motor flange-mounted to the outside face of the headstock-end leg and some perfunctory shielding of the lower belt run. By the 1950s a cabinet more suited to modern use had been devised, with the motor again flange mounted to the left-hand outside face and with complete (and safe) enclosure of all the workings. In this form, the lathe stayed in production until at least the mid-1970s--and possibly a little longer.
During its long production life, the 4L was never offered with a screwcutting gearbox, instead, both chase screwcutting and, for conventional thread generation, a very large set of changewheels was provided. By the mid-1950s if not earlier, the option of a belt drive from the end of the spindle to a worm-and-wheel reduction gearbox that gave an exceptionally slow rate of carriage feed. A second accessory was also offered that did much the same job at lower cost - an extra changewheel bracket bolted to the ordinary one that could accommodate another pair of compounded changewheels. 
Copies were made of the L.E. version of the 4L by VEF in Latvia (and used by them to manufacture parts for their famous Minox miniature camera) and by Smart and Brown in England, during and after WW2, as the Model M in Mk. 1 and Mk. 2 forms. A much more modern Boley, the 5LZ was introduced during the late 1960s - but, even so, the long-established and popular Model 4L and its variants still continued to sell..