Vannacht laat heb k het antwoord in Amerika gevonden. Dank voor het meedenken TOP!
https://www.finewoodworking.com/2011/06/02/just-plane-trivia-why-do-they-call-it-a-frog
“I had somehow thought that it was because a Bailey frog looks like a frog. I looked through a lot of books to get a definitive answer.
The most exact, and convincing, reason is found in Rodger K. Smith’s Patented Transitional & Metallic planes in America 1827 -1927.” He sent along a copy of the page.
I’m going to paraphrase the book because it does go on. It says the first inventor to use the term “frog” in reference to the handplane was Justus A. Traut, who worked for the Stanley Rule & Level Company in the late 1800s. Apparently Traut and his co-workers started calling the thing a frog because it is just behind the throat—and harkened back to the saying “I’ve got a frog in my throat.” Stanley didn’t start using the term publicly in their documents for many years.