I don’t know why I cannot scale line A or C, line B can be resized without any problems.
lines.skp (18.4 KB)
Scale wouldn’t be the right tool for changing the length of any of those three edges. Use the Move tool and move one end.
I use it to add exact length for example 5m, Move tool doesn’t let me to specify absolute dimension only relative to vertex.
How else can I specify the absolute line size ?
Select the line and then in the entity box type the exact dimension and you’ll get the result you want.
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It’s not a bug. Just not an intended use of the Scale tool. With the edges that are drawn on axis, the Scale box has no width or height. A scale box can’t be one dimensional. With the diagonal you get a 2D scale box so you can use that on the diagonal.
Why don’t you make the edge the right length in the first place?
Guido’s suggestion will work with any of those edges. It won’t work if that edge is part of a loop of edges, though. Of course you can then use the Scale tool on the face.
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I understand, thanks the explanation 
Unfortunately I chose the solution too quickly, I asked about the line, but I want the use the solution for a line part of a face e.g. a tooth of gear.
I understand it is not a bug but is very inconvenient to rotate the gear, change the line size then rotate back.
Making the edge to the right length in the first place is not an option because often it happens that it have to change the tooth bigger/smaller with some millimeters.
So Guido’s solution cannot be used, entity info box is not active! I can resize with absolute value the lines A or C but line B(that is the most essential !) cannot be modify without to rotate the entire gear. I don’t understand DaveR suggestion’s to use the Scale tool on the face, how can it be used for a single edge?
Any idea?? (no delete/redraw of course)
gear_tooth.skp (26.6 KB)
Scaling a line with Fredo Scale
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There are usually many different ways to accomplish something in SketchUp. The scale tool can be used on any 2D surface, so push-pull your gear tooth into 3 dimensions first. Then use the scale tool to adjust the dimension of the face. Select the face, use the modifier key to scale around center, start the scale operation, then let go of the mouse and type in the desired dimensions. Here I made the tooth a component and distributed it first to save time. Then I adjust the face B to 90 mm, then 80mm.
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excellent solution, thanks
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If you want to play with another method, click in sequence on the scenes tabs of this SU file.
Gear_tooth_scaled.skp (65.5 KB)
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