Damage Threshold

Damage Threshold is a combat statistic in Fallout, Fallout 2, and Fallout Tactics: Brotherhood of Steel. It was removed in Fallout 3, leaving Damage Resistance as the only armor statistic. However, it was restored in Fallout: New Vegas.

Any damage taken is reduced by this amount. Damage threshold can be increased by wearing armor.

Note, however, the difference from armor class, which helps dodge the attack, and damage resistance, which reduces damage by a certain percentage after the damage threshold.

Fallout: New Vegas
In Fallout: New Vegas, a red shield appears next to a target's health meter when you hit it for damage that is equal to or less than the target's damage threshold. A HUD-colored shield appears next to the player's health meter when the player is hit for damage equal to or less than the player's damage threshold.

The Living Anatomy perk can be used to view enemy DT values.

Damage negated in this way will never be reduced below 20% of the weapon's original damage value.

Damage which is reduced to minimum is indicated with a shield icon next to the health bar (either yours, or the enemy's, depending on who's getting damaged). If the damage would be reduced to minimum, but you're using AP rounds which negates some of the enemy's DT, then a broken shield icon is shown.

Strategy

 * Some weapons have a high DPS because they have a low damage, but a very high rate of fire. Against an armored foe with high DT, each individual hit will be reduced in damage significantly, resulting in a severe reduction in DPS.  It's better to use weapons with a high DAM against armored foes, and a high DPS against unarmored foes.

Bugs
In spite of DT being the determining factor for armor in New Vegas merchants when repairing armor will list DR instead. All armors when viewed from the repair screen have a DR of 0