Lathes badged "Harrison 11-inch" are just machines produced during the last years of L5A/L6 production; they had a 5.5" centre height but, instead of a screwed thread on the spindle nose, were supplied as standard with the safer and more rigid American L00 (L zero-zero) fitting..
Typical late-model Harrison badged as an "11-inch" and fitted with a full (Inch) screwcutting & feeds gearbox
Harrison L5/L5A/11-inch with 3-speed screwcutting and feeds gearbox
L5A/11-inch compound slide rest, 4-way toolpost on a T-slot top-slide, bed-mounted multi-stop and dial-thread indicator.
The changewheels were made from steel, not cast iron, and as a result could set up quite a ringing noise at higher spindle speeds; careful adjustment of backlash between mating teeth, and the use of a heavier, "open-gear" lubricant helped to minimise this problem.
L5A/11-inch carriage with the thicker top slide casting that allowed the use of a T-slot to retain the toolpost. This machine has the large bore, threaded headstock spindle.
North American market L5A/11-inch badged as a "Clearing"
When the increased centre height L.5A was introduced its spindle (with a slightly larger 1.375" (35 mm) hole was also offered on the smaller machine L5 - though this is rarely found.