3
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  1. Without decimal point

     Graphics3D[{Arrowheads[0.03], Black, Specularity[White, 50],
      Polygon[Join[
      Table[{0, 0, 0} + {Cos[a], Sin[a], 0}, {a, 0, π, π/6}],
      Table[{-.5 , 0, 0} + .5 {Cos[a], Sin[a], 0}, {a,
      0, π, π/6}],
      Table[{.5, 0, 0} + .5 {Cos[a], Sin[a], 0}, {a, π,
      2 π, π/6}],
      Table[{0.5, 0, 0} + 0.25 {Cos[a], Sin[a], 0}, {a, 0,
      2 π, π/6}]]]}]
    

    enter image description here

  2. With decimal point

    Graphics3D[{Arrowheads[0.03], Black, Specularity[White, 50],
        Polygon[Join[
      Table[{0, 0, 0} + {Cos[a], Sin[a], 0}, {a, 0, π, π/6}],
      Table[{-.5 , 0, 0} + .5 {Cos[a], Sin[a], 0}, {a,
      0., π, π/6}],
      Table[{.5, 0, 0} + .5 {Cos[a], Sin[a], 0}, {a, π,
      2 π, π/6}],
      Table[{0.5, 0, 0} + 0.25 {Cos[a], Sin[a], 0}, {a, 0.,
      2 π, π/6}]]]}]
    

    enter image description here

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  • $\begingroup$ This is because 0. is a floating point, and 0 an integer. It is best where possible to use integer, or at least rational numbers. $\endgroup$ – Feyre Sep 1 '16 at 8:00
  • $\begingroup$ But I am still not clear about how this difference happens. $\endgroup$ – user42305 Sep 1 '16 at 9:03
  • $\begingroup$ sometimes 0. Will be 0.00~1 or so thus leave out one point in Table, but even this cannot explain this phenomenon. I'm currently without my computer, I will check this out. :) it seems like a mathematica's misbehaviour $\endgroup$ – Wjx Sep 5 '16 at 6:54

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