What is the difference?

Cat 1 are lighter duty and usually on tractors up to around 50 hp. Cat 2 is used on tractors from the 50 to 100+ hp. The pins are a larger diameter on cat 2 to support bigger, heavier attachments. If I remember correctly the lower lift pins are 7/8 inch on cat 1 and 1 1/8 on cat 2. There are higher categories for the bigger tractors.

Cat 1 is the smaller of the 2 usually very small (8N) tractor, Cat 2 think 4020

OK. I think I got it now. Thanks.

Bender, Bender, Bender tisk, tisk, and thought I was a cheechako.
Seriously, if you don't know, ask.

My first tractor Richard. Wet behind the ears.

No crime in not knowing. Asking questions lowers the learning curve. Much better than figuring it out. Challenge is to sift through the answers to determine the most correct answer. I was in your shoes a couple of years ago. Still asking questions, too.

Of course, asking is never wrong. Just funnin' a bit.

Everybody is ignorant, only on different subjects.
Will Rogers (IIRC)

I know you're funning Richard. I'm just studying before the exam!

I got a rear hay bale spear this fall that goes on my 45hp, as well as my 100hp.

It's a Cat I & Cat II implement.

The links can be bushed up to the larger size, but the bushings can break with a hard load, like a plow.

You can get by that problem with an implement that uses step pins.

The pin itself is stronger where it attaches to a Cat II. No bushing required.

https://www.amazon.com/gp/product/B01AX3JXCY/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1