# Changing line thickness of arrow

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{arrows}

\begin{document}
\begin{tikzpicture}

\draw[step=1cm,color=gray] (0,0) grid (3,3);
\draw[draw=black,solid, -triangle 90,fill=black] (0,0) -- (0,3);

\end{tikzpicture}
\end{document}


I've tried changing this arrow with ultra thick and double, but the arrow head size changes too. I'm trying to only increase the width of the line.

I came across a similar post, but thick arc doesn't seem to work even when I add all the libraries.

In TikZ the arrow heads are often related to the line width since the arrow head placement requires some calculations to place it correctly. To be able to detach that link you can use the same path twice one thick without arrow and one thin with arrow. But you need to place it manually with shorten or do some calculation yourself depending on the line width. Again the same problem, you would get many problems if you have curves etc. You can also try the arrow heads that Luigi provided in Is it possible to change the size of an arrowhead in TikZ/PGF?

\documentclass[tikz]{standalone}
\usetikzlibrary{arrows}
\begin{document}
\begin{tikzpicture}
\node (a) at (0,0) {};
\node (b) at (5,5){B};
\path[draw=black,solid,line width=2mm,fill=black,
preaction={-triangle 90,thin,draw,shorten >=-1mm}
] (1, 4) -- (3.3, 4);
\end{tikzpicture}
\end{document}