What is (a) The enlarged part of a shaft, on which a wheel is keyed, or at the end, where it is coupled to another. (b) A swage or die used for shaping metals called?

boss — (Mech.) (a) The enlarged part of a shaft, on which a wheel is keyed, or at the end, where it is coupled to another. (b) A swage or die used for shaping metals. (Webster's 1913.)

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