The vertical structure on a forklift that lifts the forks; available in 2-stage, 3-stage, or 4-stage configurations.
Detailed Definition
The mast is the set of upright steel channels at the front of a forklift that guides the carriage and forks as they rise. Hydraulic cylinders and lift chains extend the mast sections. A 2-stage mast has two nested channels, often called duplex; a 3-stage (triplex) has three and a 4-stage (quad) has four, giving more lift height for the same collapsed height. The mast also tilts forward and back so the operator can pick up and secure loads. Mast choice sets how high the truck can stack and whether it fits through doors and into trailers.
Key mast measurements
- Maximum fork height: the highest the top of the forks can reach.
- Collapsed height: overall height with the mast fully lowered, which must clear doors, trailer openings and overhead obstructions.
- Extended height: overall height at full lift, including the load backrest, which must clear sprinklers, lights and roof structure.
- Free lift: how far the forks rise before the mast itself starts to extend.
Full free lift masts, common on triplex and quad designs, let the forks rise without the mast growing taller, which is useful inside trailers, containers and under mezzanines.
Capacity at height
A forklift's rated capacity is given at a specific load center and lift height. As the forks go higher, especially on taller multi-stage masts, the truck's stability margin shrinks and the rated capacity often drops. The data plate shows the derated capacities for the mast and attachments actually fitted. If you change the mast or add an attachment, the plate must be updated by the manufacturer or with its approval.
When planning racking, match the top beam level to the truck's lift height and capacity at that height, not just its nominal capacity.
Related Glossary Terms
Frequently Asked Questions
What is free lift on a forklift mast and when do I need it?
Free lift is the distance the forks can rise before the inner mast sections start to extend upward. With full free lift, the overall height of the truck stays the same while the forks lift, which matters when working inside trailers and containers, under mezzanines or through doorways. If you need to double-stack pallets inside a trailer, check that the free lift is high enough for the top pallet.
Does a taller mast reduce how much a forklift can lift?
Often, yes. Lifting higher raises the combined center of gravity and can reduce stability, so manufacturers commonly rate lower capacities at greater lift heights. The truck's data plate lists capacity for the installed mast, load center and attachments. Always use the plate rating for the actual height you will reach, and remember that attachments such as side shifters or clamps also reduce net capacity.