How to make this symbol?

Using \longrightarrow is too much, but \rightarrow is too short.

\documentclass{article}
\usepackage{amsmath,amssymb}

\makeatletter
\DeclareRobustCommand{\torquesymbol}{{%
  \vphantom{\circlearrowleft}%
  \mathpalette\torque@symbol\relax
}}
\newcommand{\mediumrightarrow}{\relbar\mathrel{\mkern-8mu}\rightarrow}
\newcommand\torque@symbol[2]{%
  \ooalign{%
    \hidewidth$\m@th#1\circlearrowleft$\hidewidth\cr
    $\m@th#1\mkern2mu\mediumrightarrow$\cr
  }%
}
\makeatother
\newcommand{\torque}[1]{\overset{\torquesymbol}{#1}}

\begin{document}

$\torque{M}$

\end{document}

Try this:

\documentclass{article}
\usepackage{amsmath,amssymb}

% for convenience, you may define a new command:
\newcommand{\torque}[1]{\overset{\hspace{.5em}\circlearrowleft\hspace{-.9em}\longrightarrow}{#1}}

\begin{document}
    $\overset{\hspace{.5em}\circlearrowleft\hspace{-.9em}\longrightarrow}{M}$
    or with the command:
    $\torque{M}$
\end{document}

EDIT: of course you may define a specific new command (even if egreg says that \longrightarrow is too long, and he is always right!).

One way to make the torque symbol is to use \longrightarrow and the \leftturn symbol from wasysymb.

Code:

\documentclass{standalone}
\usepackage{wasysym}
\usepackage{scalerel}
\usepackage{stackengine}
\usepackage{graphicx} % for \scalebox macro
\newcommand\torque{%
  \ooalign{
  \hss\scalebox{1}{$\leftturn$}\hss\cr%
  \hbox{\scalebox{1}{$\longrightarrow$}}}}
\begin{document}
Torque symbol
$\torque$\\
\end{document}

Yields: