Here is the Universal Attachment Mount Specification!

[California]

...And here is the formal specification for the 3-point Quick Hitch.

LSU AgCenter - ASAE standard Category 1 Quick Hitch

Click on the photo and diagram to see the details.

There is a difference between the Deere and generic versions of QH: On the Deere I-Match the height of the upper hook is fixed.

On the generic version of the QH (sold at Harbor Freight and many other places) you can move the upper hook up or down, or remove it and use an adapter that swings up/down to match the implement height.

Another difference between I-Match and generic is that the generic upper hook is closer to the QH chassis. If it is too close to fit the implement, then you need that adapter to get some clearance.

[KJM]

Just one thing I'll chuck in here - cat1 3pl on smaller tractors (like my B7100!) is sometimes made to cat0 spacing. Still uses cat1 pins etc, just the spacing changes.

On my B7100 the implement pins are set 20" apart. This is a PITA when you make your own implements with 26" spacing and then go to the tractor... 26" spaced implements can often have the pins turned inwards and attach quite happily.

Cheers
/Kevin