Inserter

An inserter is an entity that picks up items from the ground, transport belts, or inventories (chests, furnaces, assembling machines, etc.) and places them onto the ground, transport belts, or into inventories. Inserters are electrical machines (some legacy types are fuel-powered) that move items by swinging and extending an arm; they operate more slowly when energy is low. Inserters come in several functional variants: the basic inserter, fast inserter, long-handed inserter (long reach), stack inserter (bulk inserter), and variants that stack items onto belts. Different types have different rotation and extension speeds and different hand sizes, which determine how many items they move per cycle.

Inserters can pick up items from and place items onto specific lanes of a transport belt. Belts have two lanes; when placing an item, an inserter places on the far lane from the inserter’s perspective, or on the right-hand lane from the belt’s perspective if the belt runs the same or opposite direction as the inserter. When picking up, an inserter prefers the nearest lane if the belt is perpendicular; if the nearest lane is empty it takes from the far lane. If the belt parallels the inserter or is curved, the inserter prefers the left lane from the belt’s perspective and otherwise takes from the right lane. Inserters cannot put items onto a fully compressed belt (no gaps); they wait for a gap, and if the gap is narrower than the item the upstream belt flow will stop to make room for insertion.

Inserters have automatic insertion limits for certain targets to allow item sharing on belts and prevent overfilling. Examples include fuel into boilers/furnaces/burner inserters/nuclear reactors limited to five items, gun turrets limited to ten magazines, and artillery turrets limited to five shells. For machines that consume ingredients (assemblers, furnaces, centrifuges, chemical plants, refineries), inserters will provide ingredients up to the amount needed for one craft in addition to the ingredients that can be completed during one normal-quality swing, with minimums and maximums set by the game mechanics. Inserters that have a capacity bonus greater than one can overfill a target when they pick up more than the target requires; overfilling can also occur with multiple inserters inserting into the same inventory.

Inserters may fail or perform poorly in certain situations. They can struggle to pick up items from very fast belts because items move too quickly, from the entry or exit of underground belts due to shorter pickup time, and from turning belts if the item is on the inside of the corner. When two inserters try to pick up from the exact same position, the previously placed inserter has priority. Inserters cannot insert items into fixed recipe-specific slots (for example, they cannot place iron plates into the copper wire input slot of an assembling machine), cannot place items into a full inventory, cannot place multiple items on the same ground tile, and cannot exceed explicit slot limits (red-slot limited inventories).

Inserter speed is governed by rotation-speed (turns per tick) and extension-speed (tiles per tick). Rotation conventions treat one full rotation as one turn; actual ticks per full turn are adjusted to even numbers because pick-and-drop operations are performed as two half-turns. Extension-speed differences affect pickup/drop timing and are relevant when taking from near versus far sides of belts or when mods alter pickup/drop locations. Chest-to-chest and chest-to-belt throughput depends on arm cycle time, hand size, capacity bonuses, and belt fullness; stack-capable inserters can transfer whole stacks per tick in chest-to-chest transfers and greatly increase items-per-second when stacking onto belts.

• Inserters move items between belts, chests, machines, and the ground; energy shortages slow them.
• Types vary by speed, reach, and hand size: basic, fast, long-handed, stack/bulk, and belt-stacking variants.
• Inserter pickup/drop lane rules determine which belt lane is used; placement always favors the far/right lane as described.
• Automatic insertion limits and capacity bonuses control how much an inserter fills a target and prevent monopolizing belt items.
• Inserters have known pickup issues with fast belts, underground entrances/exits, and inside corners of curves.