Tricker's chukkas are available on several different lasts. Typically the 4444, 4497 or 2298.
4444 fits big (Bourton is on the 4444).
4497 is not quite as big (Stow is usually on the 4497).
2298 is more or less TTS.
There are a bunch of other lasts they use for chukkas but they're not as common but are pretty much TTS.
I wouldn't buy a pair of of Tricker's unless I knew what last it was on.
For lasts, you generally just need to know 4444 fits big, 4497 fits slightly big,...