The Health and Safety Executive (HSE) investigation found the apprentice was forming a piece of sheet metal into a radius using a three-roll bending machine when his gloved hand was drawn in by the in-running nip between two steel rollers.
The HSE found that the accident, which happened at Air Management & Design's premises on Spencroft Road in Newcastle-under-Lyme on 3 March 2018 was more likely because he was using fully fingered gloves.
The Staffordshire ductwork engineering and steel fabrication business did not operate a safe system of work, failed to provide adequate training on the machinery and did not supervise the young worker.
Air Management & Design pleaded guilty to breaching s 2(1) of the Health and Safety at Work Act at Cannock Magistrates' Court. The firm was fined £12,000 and must pay £1,301 costs.
HSE inspector Wendy Campbell said: "This is a reminder to all companies to check that fully fingered gloves are not worn, and safe systems of work are in place and being followed for operation of dangerous machinery such as three-roll bending machines."