The Flesh is Weak Non-vehicle Iron Hands models have the Feel No Pain (6+) special Rule. If they have the Feel No Pain rule from another source (a narthecium, for example), they instead add 1 to the result of any Feel No Pain rolls.
It Will Not Die At the end of each of your turns, roll a D6 for each of your models with this special rule that has less than its starting number of Wounds or Hull Points, but has not been removed as a casualty or destroyed. On a 5+, that model regains a Wound or Hull Point lost earlier in the game.
Feel No Pain When a model with this special rule suffers an unsaved Wound, it can make a special Feel No Pain roll to avoid being wounded (this is not a saving throw and so can be used against attacks that state that 'no saves of any kind are allowed', for example those inflicted by Perils of the Warp).
Feel No Pain saves may not be taken against Destroyer attacks or against unsaved Wounds that have the Instant Death special rule.
Roll a D6 each time an unsaved Wound is suffered. On a 4 or less, you must take the Wound as normal. On a 5+, the unsaved Wound is discounted - treat it as having been saved.
If a unit has the Feel No Pain special rule with a number in brackets afterwards -Feel No Pain (6+), for example - then the number in brackets is the D6 result needed to discount the Wound.