... tool joints, drill collars, casings, cables with a variety of shapes and sizes. Also, to provide ... the principle of a wedge to shut in the wellbore. It has a donut-like rubber seal, known ... thrust forces the packing unit to constrict, like a sphincter, sealing the annulus or open hole. ... ram blowout preventers. An annular blowout preventer has a rubber sealing element that, when activated, seals the ...