AR 670-1 and DA PAM 670-1. Where in the regulation does it say your hair cannot pass the length of 3in for males?

There's always some guy quoting the old outdated reg. It used to say you had to be clean shaven at all times as well. What's worse is a lot of division standards books will reference these old regs as well.

SGT (Join to see) for females it specifies length:
"(c) Long length. Long hair is defined as hair length that extends beyond the lower edge of the collar. Long hair will be neatly and inconspicuously fastened or pinned above the lower edge of the collar (except when worn in accordance with para 3–2a(j)), except that bangs may be worn. The regulations for the wear of bangs detailed in paragraph 3– 2a(3)(a) apply. No portion of the bulk of the hair, as measured from the scalp as styled, will exceed 2 inches (except a bun, which is worn on the back of the head and may extend a maximum of 3 1/2 inches from the scalp and be no wider than the width of the head)."

Where males run afoul of the standard is having longer hair on top or on the sides that do not present a tapered appearance...then of course side burns, but that is not what your question raises.

"(2) Male haircuts. The hair on top of the head must be neatly groomed. The length and bulk of the hair may not be excessive and must present a neat and conservative appearance. The hair must present a tapered appearance. A tapered appearance is one where the outline of the Soldier’s hair conforms to the shape of the head (see scalp line in fig 3–1), curving inward to the natural termination point at the base of the neck. When the hair is combed, it will not fall over the ears or eyebrows, or touch the collar, except for the closely cut hair at the back of the neck. The block-cut fullness in the back is permitted to a moderate degree, as long as the tapered look is maintained. Males are not authorized to wear braids, cornrows, twists, dreadlocks, or locks while in uniform or in civilian clothes on duty. Haircuts with a single, unta- pered patch of hair on the top of the head (not consistent with natural hair loss) are considered eccentric and are not au- thorized. Examples include, but are not limited to, when the head is shaved around a strip of hair down the center of the head (mohawk), around a u-shaped hair area (horseshoe), or around a patch of hair on the front top of the head (tear drop). Hair that is completely shaved or trimmed closely to the scalp is authorized. (See figs 3–1 and 3–2.)"

The NCO maybe cueing in on "The hair on top of the head must be neatly groomed. The length and bulk of the hair may not be excessive and must present a neat and conservative appearance. The hair must present a tapered appearance." Or as was popular among young soldiers when I came, the skate or die high fade with long hair on top where they had excessive bangs or comb over that was unkempt and notntapered. "...When the hair is combed, it will not fall over the ears or eyebrows, or touch the collar, except for the closely cut hair at the back of the neck. The block-cut fullness in the back is permitted to a moderate degree, as long as the tapered look is maintained"

https://simpsonswiki.com/w/index.php?title=Dolph_Starbeam&useformat=mobile An exaggeration....but when the rest is trimmed close and tapered and you have a longer splotch not integrated in the taper it screams counsel me.

You are correct: The 3" length reference is for females regarding the max length a bun may extend from scalp. There is also a max length of of 2" from scalp for bulk of hair (excluding bun). Further, Figure 3-3 illustrates that the longest length of hair from scalp for females is 1" for one particular style illustrated.
So, you are correct in your finding that there is no reference to a max length of 3" for males. However, this doesn't mean males can have 3" of length, as I doubt you could comply with the requirement for the hair to present a tapered appearance, and not appear extreme, ragged, or unkempt at much over 1", much less 3". Hair is one of those items that you have to see with and without headgear to determine whether it meets the requirements. Of course, the commander determines what is in compliance, or not.
I commend you for your research, and wanting to know what the regulations say, and now you can tactfully correct anyone who references the 3" as applying to males, when it is actually tapered to shape of head, and not ragged, unkempt, or extreme.

(2) Male haircuts. The hair on top of the head must be neatly groomed. The length and bulk of the hair may not be excessive or present a ragged, unkempt, or extreme appearance. The hair must present a tapered appearance. A tapered
appearance is one where the outline of the Soldier’s hair conforms to the shape of the head (see scalp line in figure 3–1), curving inward to the natural termination point at the base of the neck. When the hair is combed, it will not fall over the ears or eyebrows, or touch the collar, except for the closely cut hair at the back of the neck. The block-cut
fullness in the back is permitted to a moderate degree, as long as the tapered look is maintained.