Here's my input:
\documentclass{article}
\DeclareFontEncoding{LMP2}{}{}
\DeclareFontSubstitution{LMP2}{mtt}{m}{n}
\DeclareFontFamily{LMP2}{mtt}{\skewchar\font48}
\DeclareFontShape{LMP2}{mtt}{m}{n}{<-7> mt2syf <7-9> mt2sys <9-> mt2syt}{}
\DeclareSymbolFont{Test} {LMP2}{mtt}{m}{n}
\DeclareMathSymbol{\hslash}{\mathord}{Test}{175}
\begin{document}
Words $\hslash$ words.
\end{document}

\usepackage{mtpro2}or, if you have the really old version of the MathTime Professional package,\usepackage{mtpro}? – Mico Aug 13 '16 at 07:07