Jason,

These threaded fasteners are caused "studs." The studs used to secure many Volvo engine parts (intake and exhaust manifold, valve cover, water pump, header pipe, etc.) are special because they have an unthreaded section in the middle that (i) helps position and align the item being secured to the block, (ii) assures that the stud is threaded to the correct depth, and (iii) can be used with vise grips for removal and installation.

These are strength-graded fasteners; DO NOT use a generic stud or bolt from the hardware store. You probably should not reuse the exhaust manifold studs. They get very rusty and may break upon reinstallation. Either get new ones from Volvo (about $2 a pop), or salvage clean ones from the cam bearing caps or intake manifold on a parts car.

Good luck...!
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Six bricks, yep, six!