{"course":{"slug":"vector-and-print","title":"Vectors, Logos and Things That Get Printed","url":"https://addaly.com/learn/vector-and-print","level":"beginner","track":"create"},"lesson":{"slug":"a-path-has-no-thickness","title":"A path has no thickness","url":"https://addaly.com/learn/vector-and-print/a-path-has-no-thickness","position":4,"of":73,"minutes":9,"answer":"A stroke is a render-time instruction, not an object, so its caps, joins, miter limit and scaling behaviour can change the printed shape, and a \"hairline\" means whatever the output device's thinnest line is.","keyIdea":"A stroke is a render-time instruction, not an object, so its caps, joins, miter limit and scaling behaviour can change the printed shape, and a \"hairline\" means whatever the output device's thinnest line is, which on a platesetter is thin enough to disappear."},"body":{"format":"markdown","text":"## The line you drew does not exist\n\nDraw a line in any vector program and give it a 2 mm stroke. You now believe there is a 2 mm-wide object on the page. There is not. There is a mathematical path, a curve of zero width, and an instruction attached to it that says *when rendering, sweep a 2 mm-wide brush along me*.\n\nNothing downstream is obliged to obey that instruction the way you expect, and the places where it goes wrong are the places this lesson exists for.\n\n## The parameters that actually change the shape\n\nA stroke carries more than a width:\n\n- **Cap**: what happens at an open end. `butt` stops exactly at the endpoint. `round` and `square` extend it by half the stroke width beyond. A 10 mm line with a 4 mm round cap measures 14 mm. This is why a dimension you carefully set comes out long.\n- **Join**: what happens at a corner. `miter` extends both edges until they meet, `round` arcs across, `bevel` cuts the corner flat.\n- **Miter limit**: the escape hatch on the above. At a sharp angle, a mitred join produces a spike that can run far beyond the corner; the limit is the ratio at which the renderer gives up and bevels instead. SVG and PDF default to 4, which cuts in at about 29°. A logo with a very sharp point can therefore render with a spike in one program and a flat corner in another, and both are following the specification.\n- **Dash array**: a list of on/off lengths, in stroke units, plus an offset. Dashes are generated at render time; they are not objects.\n- **Alignment**: centre, inside or outside. Illustrator, Affinity and CorelDRAW offer all three. **SVG has only centre**, so an inside-aligned stroke exported to SVG shifts by half its width. Inkscape approximates the other two with a Live Path Effect, which does not survive export to most other programs.\n\n## Hairlines, and the line that vanishes on press\n\nCorelDRAW and several plotter drivers offer a width called **hairline**. It is not a measurement. It means *the thinnest line this output device can produce*.\n\n- On a 600 dpi office laser, that is 1/600 inch = **0.042 mm**. Visible, slightly weak, fine.\n- On a 2400 dpi platesetter, that is 1/2400 inch = **0.011 mm**. That is thinner than a press can hold ink. The line breaks into dots, or disappears.\n\nSo a hairline keyline proofs perfectly on the printer beside your desk and is missing from five thousand cartons. It is one of the classic print failures, and the mechanism is entirely in the definition of the word.\n\nUse real numbers instead. Practical minimums, worth asking your supplier to confirm:\n\n- Offset litho, positive line on white: **0.1 mm** (about 0.25 pt)\n- Offset litho, reversed out of a solid: **0.15 mm**, because ink spreads into the gap\n- Digital toner and inkjet: around **0.08 mm**\n- Screen print: **0.3 mm**, coarser on textile\n- Vinyl cutting: **1 to 2 mm**, because a human has to weed it\n- Embroidery: **1.2 mm** minimum satin width\n\n## Scale strokes, or do not\n\nEvery program has a preference deciding whether a stroke scales with the object. Both behaviours are useful and the wrong one is expensive.\n\n- **On** is what you want for a logo. Shrink the mark to 10 mm and the outline shrinks with it.\n- **Off** is what you want for a technical drawing or a die-line, where 0.25 mm means 0.25 mm at any zoom.\n\nIllustrator: Preferences ▸ General ▸ *Scale Strokes & Effects*. Inkscape: the four toggle buttons at the right end of the selection tool's control bar: the first one governs stroke width. CorelDRAW: *Scale outline with object* in Object Properties.\n\nThe failure is always the same direction. Someone designs a mark at 200 mm with a 2 mm outline, scales it to a 15 mm badge with scaling off, and the outline is now proportionally thirteen times too heavy. It looks like a blob and nobody can say why.\n\n## When to make the stroke real\n\n`Stroke to path` converts the instruction into geometry: a closed outline you can boolean, cut, engrave or stitch. It is destructive: the centreline is gone, and so is the ability to change the width by typing a number.\n\nDo it when the file is leaving for a machine, and keep the editable original. Do not do it early, because every later size change then means redrawing."},"check":{"question":"A carton design proofs correctly on a 600 dpi office laser, with a visible thin keyline around each panel. Five thousand printed cartons come back with no keyline at all. The artwork was set to CorelDRAW's \"hairline\" width. What happened?","options":[{"text":"The press ran out of registration and the keyline fell outside the trim on every sheet.","correct":false,"tempting":"Registration drift moves artwork by tenths of a millimetre; it does not remove a line from the whole run, and it would not explain the proof looking right."},{"text":"Hairline means the device's thinnest line: 0.042 mm on the laser, 0.011 mm on the platesetter, below what a press can hold.","correct":true},{"text":"Hairline is 0.25 pt, and 0.25 pt is below the 0.35 pt minimum for offset litho.","correct":false,"tempting":"Treats hairline as a fixed measurement. It is device-relative, which is exactly why the same file behaved differently on two devices."},{"text":"The keyline was a stroke rather than an outlined object, and strokes are discarded whenever a PDF is flattened for press output.","correct":false,"tempting":"Flattening affects transparency, not strokes. A stroke survives to the RIP perfectly well; the question is what width it asks for."}]},"prev":{"slug":"units-and-the-dpi-that-is-not-there","title":"Points, millimetres, and two different inches","url":"https://addaly.com/learn/vector-and-print/units-and-the-dpi-that-is-not-there"},"next":{"slug":"winding-rules-and-compound-paths","title":"Why the hole will not appear","url":"https://addaly.com/learn/vector-and-print/winding-rules-and-compound-paths"},"authorship":"Founder and series editor: Dr Mustafa Mun. Written by AI models to a written standard. Exam keys checked blind by a second model: 3,665 of 3,666 agreed. Academic review invited.","review":{"status":"Draft, open for academic review"},"cite":"Addaly (2026) 'A path has no thickness', in Vectors, Logos and Things That Get Printed. Edited by M. Mun. Addaly. Available at: https://addaly.com/learn/vector-and-print/a-path-has-no-thickness (Accessed: 13 October 2026).","licence":{"name":"CC BY-NC-SA 4.0","url":"https://creativecommons.org/licenses/by-nc-sa/4.0/"},"reader":{"schema":1,"title":"A path has no thickness","courseTitle":"Vectors, Logos and Things That Get Printed","module":{"index":1,"slug":"what-a-vector-is","title":"The thing that is actually in the file"},"answer":null,"keyIdea":"A stroke is a render-time instruction, not an object, so its caps, joins, miter limit and scaling behaviour can change the printed shape, and a “hairline” means whatever the output device’s thinnest line is, which on a platesetter is thin enough to disappear.","hero":{"kind":"plate","image":null,"alt":null,"caption":null},"blocks":[{"t":"h2","id":"the-line-you-drew-does-not-exist","runs":[{"text":"The line you drew does not exist"}]},{"t":"p","runs":[{"text":"Draw a line in any vector program and give it a 2 mm stroke. You now believe there is a 2 mm-wide object on the page. There is not. There is a mathematical path, a curve of zero width, and an instruction attached to it that says "},{"text":"when rendering, sweep a 2 mm-wide brush along me","i":true},{"text":"."}]},{"t":"p","runs":[{"text":"Nothing downstream is obliged to obey that instruction the way you expect, and the places where it goes wrong are the places this lesson exists for."}]},{"t":"h2","id":"the-parameters-that-actually-change-the-shape","runs":[{"text":"The parameters that actually change the shape"}]},{"t":"p","runs":[{"text":"A stroke carries more than a width:"}]},{"t":"ul","items":[[{"text":"Cap","b":true},{"text":": what happens at an open end. "},{"text":"butt","code":true},{"text":" stops exactly at the endpoint. "},{"text":"round","code":true},{"text":" and "},{"text":"square","code":true},{"text":" extend it by half the stroke width beyond. A 10 mm line with a 4 mm round cap measures 14 mm. This is why a dimension you carefully set comes out long."}],[{"text":"Join","b":true},{"text":": what happens at a corner. "},{"text":"miter","code":true},{"text":" extends both edges until they meet, "},{"text":"round","code":true},{"text":" arcs across, "},{"text":"bevel","code":true},{"text":" cuts the corner flat."}],[{"text":"Miter limit","b":true},{"text":": the escape hatch on the above. At a sharp angle, a mitred join produces a spike that can run far beyond the corner; the limit is the ratio at which the renderer gives up and bevels instead. SVG and PDF default to 4, which cuts in at about 29°. A logo with a very sharp point can therefore render with a spike in one program and a flat corner in another, and both are following the specification."}],[{"text":"Dash array","b":true},{"text":": a list of on/off lengths, in stroke units, plus an offset. Dashes are generated at render time; they are not objects."}],[{"text":"Alignment","b":true},{"text":": centre, inside or outside. Illustrator, Affinity and CorelDRAW offer all three. "},{"text":"SVG has only centre","b":true},{"text":", so an inside-aligned stroke exported to SVG shifts by half its width. Inkscape approximates the other two with a Live Path Effect, which does not survive export to most other programs."}]]},{"t":"h2","id":"hairlines-and-the-line-that-vanishes-on-press","runs":[{"text":"Hairlines, and the line that vanishes on press"}]},{"t":"p","runs":[{"text":"CorelDRAW and several plotter drivers offer a width called "},{"text":"hairline","b":true},{"text":". It is not a measurement. It means "},{"text":"the thinnest line this output device can produce","i":true},{"text":"."}]},{"t":"ul","items":[[{"text":"On a 600 dpi office laser, that is 1/600 inch = "},{"text":"0.042 mm","b":true},{"text":". Visible, slightly weak, fine."}],[{"text":"On a 2400 dpi platesetter, that is 1/2400 inch = "},{"text":"0.011 mm","b":true},{"text":". That is thinner than a press can hold ink. The line breaks into dots, or disappears."}]]},{"t":"p","runs":[{"text":"So a hairline keyline proofs perfectly on the printer beside your desk and is missing from five thousand cartons. It is one of the classic print failures, and the mechanism is entirely in the definition of the word."}]},{"t":"p","runs":[{"text":"Use real numbers instead. Practical minimums, worth asking your supplier to confirm:"}]},{"t":"ul","items":[[{"text":"Offset litho, positive line on white: "},{"text":"0.1 mm","b":true},{"text":" (about 0.25 pt)"}],[{"text":"Offset litho, reversed out of a solid: "},{"text":"0.15 mm","b":true},{"text":", because ink spreads into the gap"}],[{"text":"Digital toner and inkjet: around "},{"text":"0.08 mm","b":true}],[{"text":"Screen print: "},{"text":"0.3 mm","b":true},{"text":", coarser on textile"}],[{"text":"Vinyl cutting: "},{"text":"1 to 2 mm","b":true},{"text":", because a human has to weed it"}],[{"text":"Embroidery: "},{"text":"1.2 mm","b":true},{"text":" minimum satin width"}]]},{"t":"h2","id":"scale-strokes-or-do-not","runs":[{"text":"Scale strokes, or do not"}]},{"t":"p","runs":[{"text":"Every program has a preference deciding whether a stroke scales with the object. Both behaviours are useful and the wrong one is expensive."}]},{"t":"ul","items":[[{"text":"On","b":true},{"text":" is what you want for a logo. Shrink the mark to 10 mm and the outline shrinks with it."}],[{"text":"Off","b":true},{"text":" is what you want for a technical drawing or a die-line, where 0.25 mm means 0.25 mm at any zoom."}]]},{"t":"p","runs":[{"text":"Illustrator: Preferences ▸ General ▸ "},{"text":"Scale Strokes & Effects","i":true},{"text":". Inkscape: the four toggle buttons at the right end of the selection tool’s control bar: the first one governs stroke width. CorelDRAW: "},{"text":"Scale outline with object","i":true},{"text":" in Object Properties."}]},{"t":"p","runs":[{"text":"The failure is always the same direction. Someone designs a mark at 200 mm with a 2 mm outline, scales it to a 15 mm badge with scaling off, and the outline is now proportionally thirteen times too heavy. It looks like a blob and nobody can say why."}]},{"t":"h2","id":"when-to-make-the-stroke-real","runs":[{"text":"When to make the stroke real"}]},{"t":"p","runs":[{"text":"Stroke to path","code":true},{"text":" converts the instruction into geometry: a closed outline you can boolean, cut, engrave or stitch. It is destructive: the centreline is gone, and so is the ability to change the width by typing a number."}]},{"t":"p","runs":[{"text":"Do it when the file is leaving for a machine, and keep the editable original. Do not do it early, because every later size change then means redrawing."}]}],"check":{"question":[{"text":"A carton design proofs correctly on a 600 dpi office laser, with a visible thin keyline around each panel. Five thousand printed cartons come back with no keyline at all. The artwork was set to CorelDRAW’s “hairline” width. What happened?"}],"options":[{"text":[{"text":"The press ran out of registration and the keyline fell outside the trim on every sheet."}],"correct":false,"tempting":[{"text":"Registration drift moves artwork by tenths of a millimetre; it does not remove a line from the whole run, and it would not explain the proof looking right."}]},{"text":[{"text":"Hairline means the device’s thinnest line: 0.042 mm on the laser, 0.011 mm on the platesetter, below what a press can hold."}],"correct":true,"tempting":null},{"text":[{"text":"Hairline is 0.25 pt, and 0.25 pt is below the 0.35 pt minimum for offset litho."}],"correct":false,"tempting":[{"text":"Treats hairline as a fixed measurement. It is device-relative, which is exactly why the same file behaved differently on two devices."}]},{"text":[{"text":"The keyline was a stroke rather than an outlined object, and strokes are discarded whenever a PDF is flattened for press output."}],"correct":false,"tempting":[{"text":"Flattening affects transparency, not strokes. A stroke survives to the RIP perfectly well; the question is what width it asks for."}]}],"order":[0,3,1,2],"why":null},"prev":{"slug":"units-and-the-dpi-that-is-not-there","title":"Points, millimetres, and two different inches","minutes":9},"next":{"slug":"winding-rules-and-compound-paths","title":"Why the hole will not appear","minutes":9}}}