Question How to read gear numbers to order right cutter

Ok guess the tittle says it all but.....


How do I read / understand the gear number stamped in the side of a gear so I can tell which gear cutter I need to order :confused:

More specific details : I have a old atlas 10" lathe and building a new larger spindle I want to keep the gearing as is and need to make three custom gears. I have one of my spare gears in my hand (it has the correct teeth but it's the wrong size) The number on the side of the gear is 9-100-32 how do I read that number to know which gear cutter head i need to order ? I am assuming the "9" is the pitch ??? an maybe the 32 is the angle ???? and no idea what the "100" is for

someone please educate me