For hatchling milks and juveniles, I usually "pop" the snakes first, and if no hemipenes are visible I will then double check later by probing. But unless you are very familiar with both of these methods I hesitate to recommend them to people. As for a general probe size, one that is approx.1/32of an inch will work well for hatchling milks (about the size of very small paper clip) Make absolutely sure that the end of the probe has a nice smooth, rounded tip to prevent polking the delicate tissue, and have someone help you hold and control the snake while you perform this, as you probably already know it will not enjoy this!(LOL). On a hatchling Black Milk, the probe will go down to a depth of about 3/8" to 1/2" or so on a male, and approx. 3/16" for a female.This is because the female does have a slight "pocket" for her scent gland.I use my thumb to mark the probe when it reaches maximum depth for accuracy........hope this helps.................Doug

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Better to be silent and thought a fool, than to open mouth and remove any doubt!