I have a dual catalytic converter from a big industrial trucking company. I don't want to take it to the recycling place and them tell me they are only worth $20. Each when some of them go for as much as $100. Each. How can I find out if it is regular H. comb, large H comb, pellet, etc,.

Thanks

Look inside the converter to find out

What do the different ones look like or what is it I have to look for to know?

If it's off a diesel truck it's definetily not pellet, most likely large h comb.