Synergy

Synergy is a measure of how well the main parts in a gear item are working together. The synergy value applies a multiplier to some of the gear's stats. A single-material gear item will have 100% synergy, which adds no multiplier. By mixing materials, that value can be increased (or decreased if the parts are drastically different).

How Synergy is Calculated

Synergy is first based on the number of unique main parts (as in different type, not the number of items used in crafting). This has diminishing returns. Second, synergy is reduced based on the differences in tier and rarity, compared to the highest tier and rarity in the gear. With poorly matched parts, synergy can drop below 100%, weakening the item crafted, but that's difficult to pull off.

Theoretical, the max synergy value is about 131% with the formula used in version 0.3.2. In version 0.4.0, the formula is changing to reduce how quickly the curve levels off. That means more increase for the first few parts, and the max will be higher, probably 140-150%.

(TL;DR) In other words, add different parts when crafting tool heads and armor, but try to pick parts with similar tier and rarity. Matching tiers is easy enough, but odds are you won't be able to match rarity exactly most of the time.

Traits

Some traits may affect synergy. Silent Gear adds two: synergistic and crude. These two traits cancel out.

• Synergistic - Increases synergy if it is greater than 100%. If base synergy is 100% or less, it does nothing.
• Crude - Decreases synergy, regardless of the base synergy value. This trait is found on rough rods.