What do's 110 or 330 stand for in the sizing of the conibear traps

Nothing really, they're kinda like trap sizes for footholds. lower number equals smaller trap, but it doesn't convert to a inch size.
110=4.5x4.5"
220=7x7"
330=10x10"

There are several other sizes, and some have one spring, some have 2 springs. For example, a 120 is a 110 with 2 springs. A 150 is a 5x5" trap with 1 spring, a 155 is a 5x5 trap with 2 springs.

It is just the naming system some one came up with when body traps were “invented”. The basic system is used by most makers of body traps.

110, 120, 150, 155, 160, 210, 220, 280, 330, 660. I’m sure I’m missing some

Northwoods amp Herters used. 100, 200, 300.

I wonder if anyone actually still uses the 210

Some water trappers I know use it.

There was a well known WI trapper who used them for mink and rats. He was very successful using the 210. I never actually targeted mink but a 210 or even the 220 were great rat traps. Lots of times when you choke down a run with a smaller trap like the 110 you will get refusals case In fact when we lost the use of the 220 In dry land coon trails and had to go the 160. Don't sell those bigger traps short when trapping rats.

I still use 210's (single spring 7X7 BG) for baited rat sets and most water sets that don't involve an accidental beaver. Telling my age , but the first 220's I bought in the 70's were single spring and we used them for coon in trails by the water (that was in NE and Mich).