Keilim11: 5
[ה] עַקְרָב שֶׁל פְּרֻמְבְּיָא — טְמֵאָה, וּלְחָיִים — טְהוֹרִים. רַבִּי אֱלִיעֶזֶר מְטַמֵּא בַלְּחָיַיִם. וַחֲכָמִים אוֹמְרִים: אֵין טָמֵא אֶלָּא עַקְרָב. וּבְשְׁעַת חִבּוּרָן — הַכֹּל טָמֵא.
The bit of a bridle is tamei. But the cheek-pieces [are] tahor. R’ Eliezer rules the cheek-pieces tamei. And the Sages say: Nothing is tamei except the bit. But when they are joined, everything is tamei.