Fillet Gauge
Start CWI Part BStart
Free diagnosticsCWI Part ACWI Part BCWI Part C D1.1CoursesCWI Part A courseCWI Part B courseCWI Part C D1.1 courseGuidesCWI Part A: 165 questions, closed book, 10 domainsCWI Part C with D1.1: on-screen PDF, no word searchWhat the CWI exam costs in 2026: fees, retests and seminarsCWI retest rules: which parts, how many times, and what AWS asks forHow to become a CWI: eligibility, timeline and total costD1.1 for CWI Part C: edition and on-screen codeFree toolsCWI seminar and exam dates by city, 2026-27Welding symbols quiz: read the symbol, name the weldFillet weld calculator: leg, throat, area and weld metal weightFillet GaugeThe appAbout and editorial policy

Free sample · CWI Part B

Try a full lesson: Measuring welds with the inspection tool kit

This is a complete lesson from the course (module 1 of 7, Body of knowledge topic B.1.1), followed by 3 practice questions with full explanations. Nothing to sign up for.

Like the way it teaches?The course has a lesson like this for every task in AWS's content outline.

See what's in the course

What this module covers

Part B is the practical exam: 46 questions in 120 minutes, on paper at an AWS test site. You measure plastic weld replicas with an inspection tool kit and answer questions from an exhibits booklet, with the Book of Specifications supplied for the exam open in front of you. The CWI Examination User Guide has candidates take Part B first, before Parts A and C.

Practical Applications: Welding Inspection and Discontinuities carries at least 40% of the Part B weight in AWS B5.1:2025 Table 8.1, more than any other area. Almost every one of those questions starts with a number you read off a gauge. If the reading is wrong, the clause lookup that follows cannot save you.

This module teaches the tools. Module 2 teaches how to judge the reading against the book.

The kit contents and the replica format here are our understanding from general practice. Check the CWI Part B Practical Exam Info (Rev. 03.01.2024) for what you will actually be given.

Fillet weld gauges and weld size

What the gauge set looks like

A leaf-type fillet gauge set is a ring of thin blades, one blade per size. Each blade usually has two working ends:

EndUsed forWhat touches what
Stepped or square notchConvex fillets (face bulges out)Blade sits on one member, the notch corner meets the weld toe on the other
Curved or pointed endConcave fillets (face dips in)Both blade tips sit on the members, the center point reaches toward the weld face

Reading a convex fillet

  1. Check the face first. Lay a straight edge across it, or just look. Convex means use the leg end.
  2. Pick a blade close to the specified size.
  3. Hold the blade square to the weld axis, flat on one member, and slide it until it meets the toe on the other member.
  4. Fit means the notch meets the toe with no gap. Too big a blade stands off; too small a blade passes under.
  5. Measure both legs this way. The weld size of an unequal-leg convex fillet is set by the shorter leg.

Reading a concave fillet

On a concave face the legs can look full while the throat is thin. The concave end checks the throat:

  1. Put the blade tips on both members, square to the weld.
  2. If the center point touches the weld face, the weld is at least that blade size.
  3. If you can see light between the point and the face, the weld is thinner than that blade at its throat. Step down one blade at a time until the point touches.

What the exam tests here. Using the wrong end. A concave fillet measured with the leg end reads big and gets accepted when it is undersized.

Length and location

Fillet size questions often ask how much of the length is undersize, not only by how much. Use the steel rule or caliper to measure the undersize length, and note where along the replica it starts. Clause 2.4 is where structural fillet size and length tolerances live, so you will need both numbers.

The V-WAC gauge, hi-lo gauge and dial caliper

V-WAC gauge

The V-WAC (visual weld acceptance criteria) gauge is a flat plastic or metal card with several features on it. Typical ones:

  • Undercut pointer or depth scale. Zero the pointer on the base metal next to the undercut, then move it into the deepest part of the groove and read the depth.
  • Porosity circles or holes. Hold the gauge over a pore and find the smallest circle that covers it. That gives the pore diameter.
  • Reinforcement step. Read how high the weld face stands above the base metal surface.
  • Linear scale. For lengths and spacing of indications.

Read undercut at the deepest point you can find, not the first point you touch. Slide along the toe slowly.

Hi-lo gauge

The hi-lo gauge is mainly for pipe and plate fit-up. It measures:

  • Internal misalignment (high-low). Put one finger on the inside surface of each member and read the offset on the scale. A step on the inside can trap slag and leave the root short of fusion, which is why pipe work cares about it.
  • Root opening and land, with its tapered or stepped features.
  • On some models, reinforcement height and wall thickness.

On a replica you may be asked for misalignment at the root, so read the inside step, not the outside.

Dial caliper

The caliper is your most precise tool. It has four ways to measure:

FeatureMeasures
Outside jawsThickness, bead width, specimen width
Inside jawsHole or gap width
Depth rod (tail)Depth of a groove or pit
Step (end of jaws)Height difference between two surfaces

To read an inch dial caliper: read the main beam scale to the last full tenth visible, then add the dial reading in thousandths. Invented example: the beam shows 1.200 in and the dial needle is on 37, so the reading is 1.237 in.

What the exam tests here. Reading the gauge correctly, then choosing the feature that measures what the question asks for (depth, height, offset or width).

Zeroing tools and reading them consistently

Zero before every set of readings

  • Caliper: clean the jaws, close them gently and check the needle sits on zero. If not, turn the bezel to zero. If you cannot, note the zero error and correct every reading. Invented example: the caliper reads 0.003 in with the jaws closed and 0.415 in on the part. The true reading is 0.415 minus 0.003, which is 0.412 in.
  • V-WAC undercut pointer: set it to zero on flat base metal beside the area you will measure.
  • Hi-lo gauge: check the fingers read zero on a flat surface before measuring offset.

Habits that keep readings repeatable

  1. Square to the surface. A tilted gauge reads high on height and low on depth.
  2. Eye level with the scale. Parallax adds error on a dial or a scribed line.
  3. Light from the side. A low-angle light makes undercut, overlap and pores stand out on a plastic replica. Use the magnifier for small indications.
  4. Measure the worst spot, twice. Find the deepest undercut or the highest reinforcement, measure, lift the tool and measure again. If two readings disagree, take a third.
  5. Write units every time. Note inch or millimeter beside each number. Use the conversion tables (Tables 16 to 18) or Annex V if the question and your tool use different units.
  6. Do not force a gauge. Pressing a blade into soft plastic changes the reading and can mark the replica.

A quick tool routine per replica

  1. Read the label: application (structural, pipeline, pressure piping), joint and weld type.
  2. Look over the whole replica under side light and mark every indication on your scratch sheet.
  3. Measure size first (fillet gauge or caliper), then each indication with the right tool.
  4. Record each reading with units and location. Then move to the book.

Check yourself

Three questions cover which fillet gauge end to use on a concave weld, correcting a caliper reading for zero error, and choosing the tool feature for internal misalignment.

Where to look in your own books

  • CWI Part B Practical Exam Info (Rev. 03.01.2024): exam format, tool kit and replica instructions
  • AWS CWI Part B Book of Specifications (2017), clause 2.4: structural fillet weld size and length tolerances
  • Book of Specifications (2017), Annex V: formulas, conversions and fraction equivalents
  • AWS B5.1:2025 Table 8.1: the Practical Applications subject areas and their minimum weights
  • Background: AWS B1.11, Guide for the Visual Examination of Welds, for gauge use and visual examination practice

Practice set

Pick an answer in your head, then open the explanation. Every wrong option is explained too.

1. Welding Inspection and Discontinuities

A structural fillet weld replica has a face that dips inward between the toes. How should the inspector use a leaf-type fillet gauge to check its size?

  1. Use the leg end and record the longer of the two legs
  2. Use the concave end with both tips on the members and check that its center point touches the weld face
  3. Close the caliper jaws across the two weld toes and read the width
  4. Use the reinforcement step on the V-WAC gauge to read the height of the face
Hint: where to look

Think about which part of a concave fillet controls its size, and which end of the blade is shaped to check that part. Clause 2.4 covers the size tolerance afterwards.

Show answer and explanation

Answer: B. Use the concave end with both tips on the members and check that its center point touches the weld face

On a concave fillet the throat, not the legs, limits the size, so the concave end is used: tips on both members, and the center point must touch the face for the blade size to be met. The leg end reads the legs, which can look full on a concave weld, and the longer leg would overstate size even on a convex weld. Toe to toe width is not fillet size. The V-WAC reinforcement step measures height above a surface, which does not apply to a fillet's throat.

Reference: AWS CWI Part B BOS 2017 clause 2.4 (structural fillet weld size); fillet gauge practice
2. Welding Inspection and Discontinuities

With its jaws closed, a dial caliper reads 0.003 in instead of zero, and the bezel cannot be reset. The caliper then reads 0.415 in across a replica. What is the corrected measurement?

  1. 0.418 in
  2. 0.415 in
  3. 0.409 in
  4. 0.412 in
Hint: where to look

A zero error is in every reading. Decide whether the error makes readings high or low, then apply it once.

Show answer and explanation

Answer: D. 0.412 in

The caliper reads 0.003 in when the true size is zero, so every reading is 0.003 in high: 0.415 minus 0.003 equals 0.412 in. 0.418 in adds the error instead of removing it. 0.415 in ignores the error. 0.409 in subtracts it twice.

Reference: General measurement practice
3. Welding Inspection and Discontinuities

A pipe butt joint replica shows a step between the inside surfaces of the two pipes at the root. Which tool feature is designed to measure that step?

  1. The hi-lo gauge, with one finger on each inside surface
  2. The leg end of a fillet weld gauge, set against the root
  3. The porosity circles on the V-WAC gauge
  4. The outside jaws of the caliper, closed across one pipe wall
Hint: where to look

Think about what each tool in the kit is built to measure: weld size, profile, or how well two parts line up before welding.

Show answer and explanation

Answer: A. The hi-lo gauge, with one finger on each inside surface

Internal misalignment (high-low) is the offset between the two inside surfaces, and the hi-lo gauge is made to read it with a finger on each surface. A fillet gauge checks fillet legs or throat, not an offset between two members. The porosity circles size round indications. Caliper outside jaws across one wall give that wall's thickness, not the step between two pipes.

Reference: Hi-lo gauge practice; AWS B1.11 background

The CWI Part B course

Available now · instant access

Ready for the rest? The full course

  • 7modules of lessonsEvery task on the outline
  • 2full-length timed exams46 questions in 120 minutes each
  • 120practice questionsEach one explained
  • 2worked calculationsStep by step
  • 1week-by-week study planSet to your exam date
See all 7 modules
  1. Measuring welds with the inspection tool kit
  2. Judging replicas against acceptance criteria
  3. Reviewing a WPS against its PQR
  4. Checking welder qualification records
  5. Bend specimens and test results
  6. NDE in the exhibits booklet
  7. Finding your way in the Book of Specifications

Question bank and timed exams: Expert-reviewed: every question was checked by a CWI with 15 years in structural welding (2026-10-19). Every answer key is confirmed by a separate blind solve, and reported errors are fixed within 2 business days.

Questions are original and written to AWS's published content outline. Code is cited by section number so you can look it up in your own copy. Think something is wrong? Report it.