This would be hard to describe accurately for you to go off of by just telling you. It all depends on the size of the snake! Your best bet is to find someone that has a probe kit and have probed snakes before, and let them show you.
If you arent sure of which probe size to use, ask your vet, or someone who is experienced to show you in person, it really isnt easy to describe which ones to use over the internet.
Alicia Holmes www.BerkshireBoids.com
Enough snakes that i cant count them properly anymore.