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...ssembly used and the weight on the bit. The ''bottom hole assembly'', or ''BHA'', is that portion of the drill string closest to the drill bit. It consist * Subs, which are devices used to connect various parts of the BHA.

...ches small pieces of junk thrown up by turbulence. It is often part of the BHA, and it is almost always run before a core barrel or diamond bit to prevent