bell tap

bell tap

[′bel ‚tap]
(petroleum engineering)
A cylindrical fishing tool having an upward-tapered inside surface provided with hardened threads; when slipped over the upper end of lost, cylindrical, downhole drilling equipment and turned, the threaded inside surface of the bell tap cuts into and grips the outside surface of the lost equipment. Also known as bell; bell screw; bell socket; box bill; die; die collar.
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