# Parts & Weight | Big Mech Energy Idle Wiki

Parts drop rarely from defeated machines, often with rolled affixes. The tier ladder runs Nerfed → Mid → Lit → Sweaty → Based → Unit → GOATED. Drops stop at Based; **Unit and GOATED only come out of the Foundry**. Each tier multiplies the part's primary effect (×1 up to ×2.65) and rolls more affixes. Every part has a **type** (Attack, Power, Booster, Tuner, Utility, Frame), filterable in the **Mech → Parts** stash. Equip them under a **Weight** budget; every part shows its weight, and blocked equips say why (slots, Weight or CPU).

**Drop rates.** A normal kill drops a part about **2 percent** of the time early, climbing toward **8 percent** in the deep waves; bosses always drop one. Drop-rate bonuses (the [Core](/wiki/ascension/) tree, HAL-exa pets) raise that chance, never the tier. Which tier you get depends on how far the run is ramped (its wave plus chassis tier): early runs are almost all Nerfed, but a fully ramped run settles near **Mid 30 percent, Lit 38 percent, Sweaty 27 percent and Based 5 percent**, with Nerfed gone entirely. Bosses lean a little richer toward Sweaty. Lit is the workhorse tier; Based is the rare top of what drops.

**Rarity is a real multiplier.** A part's primary effect scales with rarity: Uncommon ×1.15, Rare ×1.32, Epic ×1.55, Legendary ×1.85. Rarer parts also roll more affixes (including weight reduction) and carry more ports for elaborate wiring. The multiplier is shown on every part.

Spare parts can be **scrapped** for Scrap or **upgraded** with Components. Upgrades follow **diminishing returns**: each level costs more and adds a little less than the last. The exception is the **Mech Core**, whose power compounds with every level; it is the long-run engine, so feeding it Components is never wrong. **Healing parts** (Repair Gel Pump, Nano-Swarm Hive) add hull regen as a build choice; natural regen alone will not out-heal a serious wave. (CPU and Storage limits grow through the [Compute Grid](/wiki/compute-grid/) late-game.)

**Protect the keepers.** Tap **Protect** on any part to lock it: scrap, the [Smelter](/wiki/smelter/) and the [Foundry](/wiki/foundry/) all skip protected parts, and their bulk tallies stop counting them, so a "melt all" or a fusion pile can never eat the roll you were saving. Unlock it the same way when you are ready to let it go.