Helmets:

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It is assumed that an appropriate type of head armoring will be added to the suit of armor in order to allow uniform protection of the wearer.
Wearing of a "great helm" adds the appropriate weight and restricts vision to the front 60° only, but it gives the head AC 1. <cf. D114: "It's a Hit, But Where?">
If a helmet is not worn,
    1 blow in 6 will strike at the AC 10 ,
    unless the opponent is intelligent,
    in which case 1 blow in 2 will be aimed at the AC 10 head (d6, 1-3 = head blow).


 
TYPES OF ARMOR & ENCUMBRANCE
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DMG