Thread sizes:
86-90: 5/16“x18 ¹⁾
91-Up: 1/2”x13

91-03 breather bolts.
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04+ breather bolts.
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Here is the OEM ham can without the filter.
The two bolts on either side of it are the breather bolts that go into the heads.
(and where the oil mist comes out).
With the stock configuration, the mist is vented back into the intake.

Backing plate (29367-07A)7)