Sentence:  Those familiar with drop forging are accustomed to sizing drop hammers as 1 ton or 5 ton or whatever. This measure of the size is simply the weight of the <WSD>tup</WSD>. The total weight of the helve of No 2 is about 6.4 tons. 
Meaning of the word marked with <WSD> tags:  The head of a hammer, and particularly of a steam-driven hammer.