Normally, a metal utensil used to eat with, such as a fork, requires immersion before its first use if it had been owned by a gentile. If a person has a metallic prosthetic hand which he uses to eat, meaning to place the food directly into the mouth, would this object require tevilas keilim (immersion in a mikveh)?

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    I'm thinking this should be the same as metal dental crowns. – Double AA Jun 5 '13 at 16:16
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    can dental crowns be easily removed? my understanding is that the latest prosethtic limbs are easy to remove/ replace – user2110 Jun 5 '13 at 16:22
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    If you are asking about specific kinds of prosthetics you should mention that in the question. – Double AA Jun 5 '13 at 16:23
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    Modern prosthetics have computer chips and some serious wiring, and can cost as much as a Lexis. I wouldn't put one in a mikvah. But if tevilah is a concern, should an amputee also worry about kashering a limb for Pesach? – Bruce James Jun 6 '13 at 17:56

What obligates something for immersion is that it is a utensil for eating with or preparing food with "כלי סעודה" Anything else has no obligation. See Shulchan Yoreh Deah 120:1, Aruch HaShulchan 120:30.

Example. A mohel needs to peel a orange and the only knife he has to use is his mila knife. So while yes it's a metal utensil, and yes it can be used for peeling the orange, since it's not meant for food prep or eating the knife does not need to be immersed before using it to peel the orange.

In our case since the primary purpose of the prosthetic hand is not for eating - even though that is certainly one of the things that he can do with it - it would not need tevilah. Again the key being "כלי סעודה" vs. anything made from metal used for eating.

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    The milah knife has one main purpose, which is not for food. A hand, however, is a multi-use tool that is typically used both for food and non-food activities. So the former is not a perfect precedent for the latter. Is there a direct precedent for a multi-use tool? Also, this answer would be much more valuable (and easier to investigate along the lines I suggest) if it included a source for the precedent and principle that it cites. – Isaac Moses Jun 6 '13 at 17:36
  • @IsaacMoses I assume the sources are Shulchan Yoreh Deah 120:1, Aruch HaShulchan 120:30 - should I edit in? – user2110 Jun 6 '13 at 18:06
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    @nikmasi, These are canonical-enough sources that if they indeed say what is cited here (can't check myself right now), I think you're safe editing them in. If eramm has other sources, there's always the option to edit further. – Isaac Moses Jun 6 '13 at 18:41
  • the question is what the halacha says about something like a "swiss army knive" – juanora Jun 12 '13 at 6:24

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