The ABC thing is the order in which the torches of a certain line have debuted. A is first, B is second, and so on.
As for the first letter, generally you can think of the head in proportion to the body. S is tube light, M is “P60 Host”, and C is pretty chunky. Think of the L as “large”.
hahahhaa nicely said…
Excellent description, well said & thank you. 
This question has been addressed to Convoy in the Convoy message thread before.
I remember the owner, Simon, mentioned that S = small, M = medium, L = large, T = tiny.
(eg. S2, S3, S6, S8, S9, etc ; M1 / M2 / M3 ; L2 / L4 / L6 ; T2)
there is also a “BD” series (built-in charging? not sure what the initials stand for but I’ve found reference of “BeiDou” which seems to be an earlier model, not sure if it’s related or not to the “BD” moniker though)
Size is relative though. “S” series appear to be EDC cylindrical shape (using mostly 18650 batteries, but some use 21700 like the S21A/S21B and the S11 uses 26650 battery)
The “C8” is different and does not follow the S/M/L because the “C8” form factor has been around much longer (from a different brand?) and so the “C8” stuck (notice, Sofirn has the C8T/C8A/C8K/C8G/C8F/C8S and Astrolux has C8 with a few different LED variants). The newer Convoy C8+ has a “+” to indicate a slightly different body design than the previous more common C8’s.
the “21” series are the newer naming that use 21700 battery (eg. S21A / S21B / L21A / M21A / M21C)
“26” uses 26650 battery. (the S11 is an earlier model that doesn’t follow this naming convention)
(eg. M26C)
M21B = similar head size as the M1 or M2, but uses 21700 battery tube (head is smaller than C8)
M21A = basically a “21700” battery version of the C8
M21C = this is bigger size, right in between the C8 and L2
Thanks d.t.a… very good info.
I think the confusing part is that every brand is different.
Ford has the F150, F250, F350
Dodge has the 1500, 2500, 3500
You have an idea what is going on without ever seeing the trucks.
Agree somewhat. And acknowledge that Chevy follows the Dodge naming of 1500/2500/3500 .
The puzzling part is that the F150/1500 is a half-ton truck, the F250/2500 is 3/4 ton, and F350/3500 is 1 ton…… So why not F50/500 for half-ton, F75/750 for 3/4 ton, and F100/1000 for 1 ton? That makes a little more sense to me.
Since a ton = 2000 lbs you could follow that a half-ton would be a F100/1000, a 3/4 ton truck would be a F150/1500, and a 1 ton truck would be a F200/2000.
Sometimes logic just doesn’t apply.
.
I guess it’s not an exact science .
Exceptional post and explination!
Good info d_t_a! And a nice collection of Convoys!