This vintage tool is stamped "Guelon, France." I believe it is some type of zester, but I cannot find an image of it anywhere online, nor any info on it.
Please help me and, if you can, tell me its specific use and possible decade(s) when it was sold. The image I have added here is the tool shown on its side.
The tool is 7" long overall and the diameter of the round head is 1.5".