I use that size probe for babies. You do need to get a better probe set because that probe is a little small for a snake that size. And don't ever use the tiny tiny probes in that set for BPs. They are much too small for any size BP. I have 2 very thin ones in my set and I've considered throwing them away since I don't think I'll ever have a need for them.
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*Factoid: "There are no such things as Hogg Island or Columbian boas"