As we learned on yesterday’s daf, the first Mishna in the perek lists utensils that are ordinarily used for activities that are forbidden on, but can be used for activities that are permitted on. One example was a hammer, which can be used to crack nuts on.
On today’s daf the Gemara explains that there is no prohibition because,
using an object whose primary function is for a prohibited use, for the purpose of utilizing the object itself to perform a permitted action, is permitted.
Nevertheless, there is a disagreement among the amora’im regarding the type of hammer that may be used for a permitted purpose.
Although the goldsmith is particular about ensuring that the hammer remains smooth and avoids using it for any purpose other than its particular use, nevertheless, it was allowed to be used for other permitted actions.
Rav Shemen bar Abba said: It was with regard to the hammer of spice merchants that we learned it may be used to crack nuts.
The Gemara explains: The one who said it is permitted to crack nuts on using the hammer of spice merchants, all the more so that it is permitted to use a hammer typically used by goldsmiths. However, the one who said that it is only permitted to use a hammer used by goldsmiths, but with regard to the hammer of spice merchants, the merchant is particular about it and would not allow it to be used for cracking nuts.
According to this opinion, use for other purposes would cause the hammer to absorb foreign smells, which would ruin the spices.