1 Some of the icons have blurred fringes at the edges of the square, which happens because another icon is too close in icons.svg and its edge's antialiasing gets into the neighboring icon. Watch out for this.
2 I don't like the thick white "midline" in these icons. What does it represent? Why white? If you want to show the midline axis, just a single solid black stroke, solid or dashed, is enough. The white is too salient and confusing.
3 I also don't like the highlights on the icons. Hey, this is just strokes! They are not supposed to be highlighted or shaded in any way. It's just silly. I have to spend extra milliseconds every time I try to figure out the join shape, dazzled by all the highlights and the white thing in it.
3 The butt cap icon is wrong: the white midline (of whatever this is) must not and can not extend beyond the stroke itself. Never.