The blade of a knife used with Chametz needs Hagalah (Roschin), as we see in the Gemara, because it is Bolei'a Chometz when used with Chametz when either the knife or the Chametz is warm. Any handle used directly with Chametz would have the same Din as the knife itself.

Handles that have not come directly in contact with Chametz may need Hagalah for two possible reasons. Firstly, if they were Bolei'a Chametz as an extention of the blade and secondly because we are worried that warm Chametz may have splashed on them at some time (Mishnah Berurah 451:68).

The first reason applies only to knives made of metal where the handle and the knife are both one piece and not two pieces connected. A handle connected to a blade, would not be Bolei'a from the blade since they are considered like two separate vessels, and we hold Belios do not travel from one vessel to another without a liquid to transfer them (Mor u'Ketzeyah 451:12and Rebi Akiva Eiger on Shulchan Aruch OC 451 on Magen Avraham 24).

The second reason would be valid to necessitate Hagalah on the handle.

There is, however, disagreement amongst the Poskim as to whether Hagalah works on plastic. Minchas Yitzchak (3:67) is of the opinion that it does, whereas Rav Moshe Feinstein (OC 2:92) disagrees.

In any event, those who wish to do Hagalah on a knife with two parts must take great care to ensure there is no dirt in the area where the two parts of the knife connect (Shulchan Aruch OC 451:3 see also Sha'ar ha'Tziyon 28).

Furthermore if there is a chance of the plastic becoming damaged through the Hagalah we would not permit this vessel to be Kashered in this way.

There is a Chumrah on Pesach, that if possible one does not do Hagalah but one buys new utensils (Mishnah Berurah 451:19).

These Halachos are very complicated and a competent Halachic authority should be consulted for any practical question, as there are many details which need to be taken into account.

Dov Freedman