Weld symbol
Finish method symbols
A single letter written with a contour symbol names how the weld face is brought to that shape - grinding, machining, chipping, rolling, hammering, or an unspecified method.
Reads asArrow side: fillet weld, 3/8 size, flush contour, finish method G.
How to read it
A finish letter never appears alone. It always accompanies a contour symbol, because the contour says what shape the face should end up and the letter says how to get it there. Reading a letter with no bar or arc beside it means something has been left off the drawing, and it is worth resolving before anyone starts dressing a weld.
The letters in common use are compact and mostly self-evident once you know the set. G stands for grinding, M for machining, C for chipping, R for rolling, and H for hammering. A U says the method is unspecified, which is a deliberate statement rather than an omission: it tells the fabricator that any method producing the required contour is acceptable.
The distinction between the letters is not cosmetic. Grinding removes metal fast and leaves directional marks that matter on fatigue-loaded joints, machining gives a controlled surface but needs access and setup, and hammering or rolling work the surface cold rather than removing material, which changes the residual stress at the weld toe rather than just its shape.
Where a drawing gives no finish letter at all, the shape is expected to come from the welding itself. That is achievable for a convex face, often achievable for a concave one, and rarely achievable for a truly flush face on any process that leaves reinforcement. Seeing a flush contour with no letter is a reason to ask a question rather than to assume grinding is intended.
Where each dimension goes
- Letter position
- Written just beyond the contour symbol on the same side of the reference line, so it applies to that side's weld face.
- G
- Grinding - fast material removal that leaves directional marks worth orienting deliberately on fatigue-loaded joints.
- M
- Machining - a controlled cut giving a predictable surface where access and setup allow.
- C, R, H
- Chipping, rolling, and hammering. The last two work the surface cold rather than removing metal from it.
- U
- Unspecified method: any technique that produces the required contour is acceptable.
Worked examples
Each one is a drawing, the sentence it comes out as, and then the mark-by-mark account of why. Read the sheet first and say the sentence yourself before you look down.
Example 1: Machined flush groove weld
TitleMachined flush groove weldRefFinish methodsEx1 / 2Reads as
Fill the vee and machine the face flush with the surrounding plate.
Which mark says so
- V-groove symbolBelow the reference lineA V-groove weld on the arrow side of the joint
- 1/2Left of the symbolGroove weld size - how deep the weld itself goes
- 60°Beyond the outer face of the symbolIncluded angle the joint is prepared to
- flush contourBeyond the outer face of the symbolThe completed face is to be flush
- MBeyond the contour on the symbolThe method used to reach that contour, not the finish itself
The bar beyond the symbol sets the flush shape and the M names machining as the method, which suits a face that has to be flat and dimensionally controlled.
And what it does not say
- No length is given, so each weld runs the full length of the joint.
- Nothing sits above the reference line, so the far face of the joint stays bare.
- There is no circle at the elbow, so the weld does not continue around the joint.
Example 2: Concave fillet with the method left open
TitleConcave fillet with the method left openRefFinish methodsEx2 / 2Reads as
Give this fillet a concave face by whatever method suits the shop.
Which mark says so
- fillet symbolBelow the reference lineA fillet weld on the arrow side of the joint
- 5/16Left of the symbolLeg size of the fillet
- concave contourBeyond the outer face of the symbolThe completed face is to be concave
- UBeyond the contour on the symbolThe method used to reach that contour, not the finish itself
The concave arc sets the shape and the U says the method is unspecified, so welding technique, grinding, or anything else producing that contour is acceptable.
And what it does not say
- No length is given, so each weld runs the full length of the joint.
- Nothing sits above the reference line, so the far face of the joint stays bare.
- There is no circle at the elbow, so the weld does not continue around the joint.
Common mistakes
- Writing a finish letter with no contour symbol, which leaves the required shape undefined.
- Reading U as an omission rather than as a deliberate statement that any method is acceptable.
- Grinding across the direction of stress on a fatigue-loaded joint where the marks themselves matter.
- Assuming a flush contour with no letter can be achieved by welding technique alone on any process.