Before us is Mishnah 6 in chapter 5 of Maseches Shevi'is, which deals with the question of which tools a craftsman is permitted to sell during the Shemittah year. The Mishnah concerns a person who is suspected of not observing the laws of Shevi'is, and the question of when selling to him is considered assisting a transgressor and when it is not.
"Eilu keilim she'ein ha'uman rashai limkoran bashevi'is":
The Mishnah lists the tools that a craftsman may not sell during Shevi'is to someone suspected of not keeping its laws:
"Macharaishah v'chol keleha" - the plow and all its accompanying implements, because the buyer will use them for plowing.
"Ha'ol" - the yoke, which also serves the needs of plowing.
"V'hamizreh" - the winnowing fork, with which grain is winnowed.
"V'hadeker" - a hoe, which was used in the process of planting and the like.
"Aval mocher hu":
In contrast to these, the craftsman is permitted to sell him the following tools:
"Magal yad" - a very small sickle, used for household needs only.
"U'magal katzir" - even a sickle that is actually used for harvesting.
"Va'agalah v'chol keleha" - a wagon and all its accessories.
The reason for the leniency: these tools can be used to bring in the small quantities of ownerless produce available during Shemittah, and they are not necessarily designated for something that the buyer will use to transgress and violate the laws of Shevi'is.
The rule established by the Mishnah:
The Mishnah sums up: "Zeh k'lal: kol shemelachto meyucheded la'aveirah - assur; l'issur ul'heter - mutar":
"Kol shemelachto meyuchedes la'aveirah - assur" - any tool whose manner of use is designated exclusively for something that is a transgression, such as the tools used for plowing, may not be sold.
"L'issur ul'heter - mutar" - a tool that can be used both for something forbidden and for something permitted, such as the sickle, which can be used for forbidden harvesting but also for permitted use, may be sold, and we assume that the buyer will use it for a permitted purpose and not for a forbidden one.
In summary: In this Mishnah we learned the parameters of selling tools during Shevi'is to someone suspected of transgressing its laws: tools whose entire use is designated for transgression - the plow and its implements, the yoke, the winnowing fork and the hoe - may not be sold; whereas tools that may also be used for a permitted purpose - a hand sickle, a harvesting sickle, and a wagon with all its accessories - are permitted, since they can be used for permitted needs and for bringing in ownerless produce. And this is the rule the Mishnah established: if its use is designated for transgression, it is forbidden; if it serves both a forbidden and a permitted purpose, it is permitted.