First, T-25a versus T-25b, and who makes which
SMACNA’s HVAC Duct Construction Standards describe two roll-formed transverse joints. T-25a is the TDC (Transverse Duct Connector) profile that Lockformer introduced in 1982; T-25b is the TDF (Transverse Duct Flange) profile that Engel introduced the same year. Both take a slip-on cleat and four corner pieces; they are not interchangeable with each other, but each is a standard, so cleats and corners for a given profile come from many suppliers and duct from any properly built machine mates with duct of the same profile.
The four machine families: Engel TDF T25B and Lockformer TDC T25a are both Mestek Machinery brands, built in Cedar Rapids, Iowa and sold through one US and Canadian dealer network; Vicon TDX (T-25b) and TDX-II (T-25a) come from Vicon’s Pevely, Missouri plant and, since February 2024, the Lindab group; Taokron SBTDF formers are our machines, and we also offer a TDC former. So a Lockformer-versus-Engel tender is one owner, and a Vicon quote is now a Lindab quote.
The comparison table
| Machine | Profile | Gauge range | Stations | Speed | Drive | Owner |
|---|
| Engel TDF T25B (18 ga model) | T-25b TDF | 18–26 ga (1.3–0.5 mm) | 16 | 75 ft/min (23 m/min) | Not stated | Mestek |
| Engel TDF T25B (16 ga model) | T-25b TDF | 16–24 ga (1.6–0.6 mm) | 16 | 50–60 ft/min (15–18 m/min) | Not stated | Mestek |
| Lockformer TDC T25a (18 ga model) | T-25a TDC | 18–26 ga | 12 | 60 ft/min (18 m/min) | Not stated | Mestek |
| Lockformer TDC T25a (16 ga model) | T-25a TDC | 16–24 ga | 16 | 70 ft/min (21 m/min) | Not stated | Mestek |
| Vicon TDX | T-25b TDF | 18–26 ga (16 ga option) | 16 | 70 ft/min (21 m/min) | 7.5 hp, oil-bath gear reducer | Lindab |
| Vicon TDX-II | T-25a TDC | 18–26 ga | 12 | 50 ft/min (15 m/min) | 5 hp, oil-bath gear reducer | Lindab |
| Taokron SBTDF-12 | TDF, 35 ± 0.5 mm flange | 0.5–1.2 mm (about 26–18 ga) | Roll-forming stations, see catalog | About 10 m/min (33 ft/min) on 1.2 mm, factory data | 2.2 kW | Taokron (independent) |
| Taokron SBTDF-1.5-16 | TDF, 35 ± 0.5 mm flange | 0.8–1.5 mm (about 22–16 ga) | Roll-forming stations, see catalog | About 8.5 m/min (28 ft/min) on 1.5 mm, factory data | 4 kW | Taokron (independent) |
Brand and product names are the property of their respective owners, referenced here for honest comparison only. Ownership, positioning and published ranges are as verified in September 2026 from each maker’s own publications; confirm current specifications and support with each vendor before buying.
Speeds are the makers’ stated forming speeds; the Taokron figures are factory test data at the top of each machine’s gauge range rather than a catalogue headline, which is why they read lower than the brochure numbers of the US machines. Real shop throughput on any of these machines is set by how fast blanks are fed and turned, not by the roll speed; a 16-station former at 75 ft/min waits for the operator most of the day.
What the differences mean in the shop
- Profile decides your consumables. Once you form T-25a you buy TDC cleats and corners; T-25b means TDF cleats and corners. Both are available from many suppliers, but a shop cannot mix them on one job. Pick the profile your local market and your existing duct use, then pick the machine.
- Gauge coverage. The 18 ga class covers 26–18 ga (roughly 0.5–1.3 mm) and suits most commercial duct; the 16 ga class covers heavy commercial, hospital and industrial duct. Taokron splits the same way: SBTDF-12 to 1.2 mm, SBTDF-1.5-16 to 1.5 mm. Buy the heavier machine if 16 ga appears in your specifications at all.
- Certification claims. Engel states its T25B formers are certified to SMACNA DCS T-25b by laboratory test and Lockformer claims T-25a certification for its TDC; Vicon states its profile meets SMACNA standards. Taokron builds to the SMACNA TDF geometry with a 35 ± 0.5 mm flange and supplies a measured sample joint; ask every vendor for a formed sample and check it against the cleats you will buy.
- Stations and adjustment. More stations spread the forming load and reduce galvanising damage; Vicon and Engel state no adjustment between gauges in range. Ask any vendor how gauge changes are handled and how long a changeover takes.
- Dealer geography. Mestek and Vicon publish North American dealer networks; outside them you buy through export channels. Taokron ships and commissions to 100+ countries with direct engineer support.
- Buying with the line. All four makers sell the flange former as part of a coil line; on a Taokron SBAL-V or SBAL-III line the SBTDF former, TDF bending machine for corners and corner making machine come from one vendor and one commissioning team.
Where Taokron fits
This is our own entry, so read it as a vendor’s case. Taokron is an Australian supplier that has built HVAC duct machinery since 1995, with 5,000+ machines in 100+ countries, ISO 9001:2015 and CE certification and catalog-accurate published specs. The SBTDF-12 and SBTDF-1.5-16 cover the same two gauge classes as the US machines at export-competitive capital cost, form the standard 35 mm TDF flange that takes off-the-shelf cleats and corners, and we publish factory-measured speeds rather than a headline. We also make the TDC former for T-25a markets, the TDF bending machines that close the corners and the auto corner making machine that produces them. Best for: shops outside the North American dealer maps, and anyone buying the former with the line, who want standard-profile flanges with direct engineer support. Weigh: our stated speeds are lower than the US brochures; ask us and them for throughput on your blanks, not roll speed.
Ask for a TDF former quotation with your gauge and profile →
FAQ
What is the difference between TDF and TDC?
Both are roll-formed transverse duct flanges joined with a slip-on cleat and four corners. TDC is the SMACNA T-25a profile introduced by Lockformer in 1982; TDF is the T-25b profile introduced by Engel the same year. They take different cleats and corners and are not interchangeable with each other, but each is a standard that many suppliers and machine makers support.
Are Engel and Lockformer flange machines from different companies?
No. Both are Mestek Machinery brands built in Cedar Rapids, Iowa and sold through the same dealer network. Mestek positions the Engel T25B as its TDF machine and the Lockformer T25a as its TDC machine.
Which machine is fastest?
On stated roll speed, the Engel 18 ga T25B at 75 ft/min, then Vicon TDX and Lockformer 16 ga TDC at 70 ft/min. In the shop, throughput is set by feeding and turning blanks, so the difference between 60 and 75 ft/min rarely shows up in ducts per shift. Ask for throughput on your blanks.
Will cleats and corners from my current supplier fit duct flanged on a different brand of machine?
Yes, if the profile is the same (T-25a to T-25a, T-25b to T-25b). Ask the new vendor for a formed sample and test your cleats and corners on it before buying.
Do I need the 16 gauge machine?
If 16 ga (1.5 mm) appears in your specifications at all, yes; 18 ga class machines stop at 18 ga (1.3 mm). Taokron splits the same way: SBTDF-12 to 1.2 mm, SBTDF-1.5-16 to 1.5 mm.
Does Taokron make a TDC machine as well as TDF?
Yes. The SBTDF formers make the TDF flange; a separate transverse duct connector (TDC) former is offered for T-25a markets, along with the TDF bending machines and the auto corner making machine.
