Gear (3.5e Creature Subtype)
From D&D Wiki
This subtype pertains to the 'Gear' family of constructs, beings of gears and clockwork that give them certain strengths and weaknesses..
The traits listed here override the base Construct traits wherever applicable.
Gear Body (Ex): Unlike normal constructs, a Gear's body is susceptible to critical hits and sneak attacks and is not immediately destroyed when reaching 0 hp. When a gear construct goes into negative hit points, they go into maintenance mode, which is equivalent to dying. They are dead when they reach -10 hit points. Alternatively, if using the Dying 3.75 variant rule, they may use their reinforced plating bonus (if applicable) as a substitute Constitution modifier for the sake of calculating maximum negative hit points.
Customizable: A Gear's body can be customized in multiple ways. The two different types of customizations are known as upgrades and grafts. An upgrade is a more passive alteration to the Gear's body that usually improves a single aspect of its body, such as defense or special resistances, without directly interfering with the body's composition. A graft on the other hand alters part of the body's substructure to such an extent that the part that is altered loses certain abilities, takes certain penalties or can no longer be used in normal manners. Grafts apply to several key areas of the body; head, arms, legs and torso. Although torso-grafts are usually the least intrusive, the side effects of most grafts are penalties to certain skills, ability scores or other statistics. Valid examples of grafts would be a head-graft that grants blindsight in exchange for conventional sight or an arm graft that changes one arm into a spell cannon at a -2 penalty to Dexterity and the cost of losing the ability to make Dexterity based skill checks related to that arm.