T-joint: meaning and how to check it

Use this diagram

Copy this HTML to show the diagram with a credit link<img src="https://filletgauge.com/charts/filletgauge/t-joint.svg" alt="Two T-joints drawn end on: an upright plate on a base plate with a fillet at each toe, and an upright plate with one lower edge beveled, filled with a groove weld and covered by a reinforcing fillet" width="100%"><p><a href="https://filletgauge.com/guides/t-joint?utm_source=embed&amp;utm_medium=referral&amp;utm_campaign=figure_embed&amp;utm_content=t-joint.svg">Same joint type both times. The weld is what changes. by Fillet Gauge</a></p>

How to recognise a T-joint

1. Find the edge and the face. One member's edge sits against the other member's flat face, somewhere away from that face's edges. That's the core of a T.
2. Check the angle. It's usually close to 90 degrees. A skewed T, where the stem leans, is still a T-joint; the angle changes how the fillet legs are sized and measured.
3. Check where the stem lands. If the stem lands right at the edge of the other plate, the end view looks like an L and you have a corner joint instead.
4. Read the weld. Fillets on one or both sides are the most common. A bevel or J on the stem with a reinforcing fillet over it is used when the joint has to carry more load through its full thickness.

Common mix-ups

• T-joint versus fillet weld. The T is the joint. The fillet is one weld you can put in it. A drawing can call a T-joint with a groove weld and no fillet at all.
• Which leg is which. On a T with a fillet, one leg runs up the stem and one runs along the base plate. Both are measured from the root, the inside corner, out to the toe. The fillet weld leg page shows how to tell an unequal-leg fillet from a sloppy equal one.
• Two sides, one joint. Fillets on both sides of the stem are two welds on one T-joint, not two joints.

T-joints on the CWI exam

Joint types are part of Definitions and Terminology, at least 12% of the closed-book Part A. Expect to name a joint from a drawing, and to tell the joint from the weld that fills it.

Part B's plastic replica set includes a T-joint. You measure its fillet legs, convexity and undercut with the gauges in the supplied kit, so the joint and its parts need to be second nature before you open the case. Welding Inspection and Discontinuities is at least 34% of the practical.

On a D1.1 Part C, fillet welds in T-joints show up across design (Clause 4), prequalification (Clause 5) and fabrication (Clause 7). Look the details up in your own copy; nothing from the code is quoted here.

Practice it

Run a few fillet sizes for a T-joint through the fillet weld calculator to see how leg size turns into throat and weld metal per foot. Then compare the other joint shapes in the welding terms glossary, or see how the symbol for a T-joint fillet reads on the fillet weld symbol page.

Know your joints? Check the rest of Part A

Take the free 10-question check. It's weighted to the Part A outline, scored by domain and needs no signup, so you see which domain costs you the most points. The Part A course then gives you a lesson on every exam subject, two full-length timed practice exams, and a worked explanation with every answer.

Sources

Show the list

• AWS bookstore, terminology and symbols listing, American Welding Society. Retrieved 20 Oct 2026.
• CWI Part A Fundamentals Examination Information, American Welding Society, Rev. 03.01.2024. Retrieved 20 Oct 2026.
• AWS B5.1:2025, Specification for the Qualification of Welding Inspectors, American Welding Society, Tables 5.1 and 8.1. Retrieved 20 Oct 2026.