Everything Ontario apprentices need to know about eligibility, booking, in-school training, and what happens after you pass the Industrial Mechanic (Millwright) 433A exam.
mwredsealprep.ca · Skilled Trades Ontario
Ontario is home to one of the largest millwright workforces in Canada, with significant employment in automotive, nuclear, pulp and paper, food processing, and general manufacturing. If you're completing your millwright apprenticeship in Ontario, here's everything you need to know about writing your Red Seal exam.
Millwright certification in Ontario is managed by Skilled Trades Ontario (STO), which replaced the Ontario College of Trades in 2021. STO oversees apprenticeship registration, hour tracking, in-school training, and exam authorization for all compulsory and voluntary trades in the province.
Compulsory Trade
Industrial Mechanic (Millwright) — trade code 433A — is a compulsory certified trade in Ontario. You must hold a Certificate of Qualification to work as a millwright in the province.
To be eligible to write the Red Seal exam in Ontario, you must have completed:
8,000 hours of on-the-job apprenticeship training (typically 4 years at ~2,000 hours per year)
In-school technical training periods at an approved college — the number and structure varies depending on how your apprenticeship is sponsored
Sign-off and recommendation from your sponsor employer or journeyperson
Union-affiliated apprentices (through a hall such as UA, IAMAW, or Local millwright unions) typically complete three blocks of in-school training: Basic, Intermediate, and Advanced. Non-union or direct-employer apprentices may follow a different structure depending on their sponsor and training provider. If you're unsure how many periods apply to your situation, confirm directly with Skilled Trades Ontario or your union training coordinator.
Your hours must be logged through the Skilled Trades Ontario apprenticeship system. If you're unsure of your recorded hours, log into your STO account at skilledtradesontario.ca to check your status.
Ready to start preparing for your 433A exam?
Practice with NOA-weighted Red Seal–style questions — free to start.
Confirm Your Eligibility with Skilled Trades Ontario
Contact STO to confirm all your hours and training levels are recorded and that you are eligible to write. You can do this through your online STO account at skilledtradesontario.ca or by calling their client services line.
Receive Your Authorization to Test (ATT)
Once STO confirms your eligibility, they will issue you an Authorization to Test (ATT). This is your permission to schedule the exam. You cannot book a testing appointment without it.
Book Through the STO Portal
Skilled Trades Ontario now delivers certifying exams in-house and manages the full exam-day experience directly. Once you have your Authorization to Test letter, follow the instructions it contains.
Exam Day
Bring two pieces of valid government-issued ID — one must include a photo. Arrive at least 15 minutes early. The exam is computer-based and takes up to 4 hours.
If you have completed your apprenticeship and are writing for the first time, your first exam attempt is typically covered at no cost through Skilled Trades Ontario — confirm your eligibility for this when you contact STO for your Authorization to Test.
First attempt (completed apprenticeship)
Typically free
Each subsequent attempt
$150 + HST
Confirm your specific fee situation directly with Skilled Trades Ontario at skilledtradesontario.ca before booking, as fees and eligibility are subject to change.
Ontario millwright in-school training is delivered at colleges across the province. Union-affiliated apprentices typically complete training structured as Basic, Intermediate, and Advanced — with Advanced being the most directly relevant to Red Seal exam content. Regardless of how your program is structured, the final period of in-school training is where NOA-level knowledge is consolidated and where your exam preparation should intensify.
Approved colleges include:
Nuclear sector apprentices
Your hands-on experience is exceptional but may be narrow in scope. Nuclear environments use highly specialized equipment. Budget extra study time for areas outside your day-to-day work — particularly fabrication, fluid power, and general rigging.
Automotive sector apprentices
High-volume manufacturing gives strong experience in specific areas (conveyors, presses, transfer lines) but may leave gaps in hydraulics, pump work, and machinery alignment.
Multi-employer apprentices
If you worked across several employers, verify that all hours from each employer are recorded in your STO file. Hours not submitted by an employer can delay your eligibility.
Skilled Trades Ontario issues your Ontario Certificate of Qualification (C of Q)
The Red Seal endorsement is added, recognizing your certification interprovincially across Canada
You are entitled to use the Interprovincial Red Seal and work as a certified Industrial Mechanic (Millwright) in any Canadian province or territory that recognizes the Red Seal program
Your certificate does not expire and does not require renewal.
If you don't achieve the 70% pass mark:
Last updated: June 2026 · Based on Skilled Trades Ontario requirements for Industrial Mechanic (Millwright) 433A
Practice with NOA-weighted Red Seal–style questions covering all six Major Work Activities on the 433A exam.
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