A "true" probe is a brass rod, 6 inches long or so, set in a plastic or wood handle. The brass doesn't scratch like steel does and transmits better feel when you touch the coin.
Over the years, I've looked all over the house for mine. Still haven't found it.
Haven't found one at any of the big box home improvement stores either. For right now, I use a lightly modified "v slot" nail puller. the tool looks like a screw driver with the flat head curved slightly and a v notch in it for pulling nails. I just smoothed the edges a little and use it like that. It doesn't give you the feel of the brass rod...But, any port in a storm. A screwdriver will do the same thing.
The probe is used for lifting coins out of the ground from a depth of up to about an inch and a half deep, without cutting a plug. Pinpoint the coin with a pin pointer. Insert the probe until you feel the coin, then maneuver the probe under the coin. Using the probe, lever the coin out of the ground (pop it out). I hunted a soccer field this morning, and used the probe for probably 70% of my coins.
A word of caution: if you are hunting where you may find older coins, don't use a steel probe!
If my daughter ever brings back the last working digital camera with close focus ability, I'll get some pictures up of the probe I'm using and the damage it can do to copper pennies.
HH