\documentstyle{article}

\newcommand{\testchars}{
\symbol{"20}
\symbol{"21}
\symbol{"22}
\symbol{"23}
\symbol{"24}
\symbol{"25}
\symbol{"26}
\symbol{"27}
\symbol{"28}
\symbol{"29}
\symbol{"2A}
\symbol{"2B}
\symbol{"2C}
\symbol{"2D}
\symbol{"2E}
\symbol{"2F}
\symbol{"30}
\symbol{"31}
\symbol{"32}
\symbol{"33}
\symbol{"34}
\symbol{"35}
\symbol{"36}
\symbol{"37}
\symbol{"38}
\symbol{"39}
\symbol{"3A}
\symbol{"3B}
\symbol{"3C}
\symbol{"3D}
\symbol{"3E}
\symbol{"3F}
\symbol{"40}
\symbol{"41}
\symbol{"42}
\symbol{"43}
\symbol{"44}
\symbol{"45}
\symbol{"46}
\symbol{"47}
\symbol{"48}
\symbol{"49}
\symbol{"4A}
\symbol{"4B}
\symbol{"4C}
\symbol{"4D}
\symbol{"4E}
\symbol{"4F}
\symbol{"50}
\symbol{"29}\symbol{"51}\symbol{"39}
\symbol{"52}
\symbol{"4D}\symbol{"53}
\symbol{"4D}\symbol{"54}
\symbol{"4D}\symbol{"55}
\symbol{"4D}\symbol{"56}
\symbol{"4D}\symbol{"57}
\symbol{"4D}\symbol{"58}
\symbol{"4D}\symbol{"59}
\symbol{"5A}
\symbol{"5F}
\symbol{"60}
\symbol{"61}
\symbol{"62}
\symbol{"63}
\symbol{"64}
\symbol{"65}
\symbol{"66}
\symbol{"4D}\symbol{"67}
\symbol{"4D}\symbol{"68}
\symbol{"4D}\symbol{"69}
\symbol{"4D}\symbol{"6A}
\symbol{"4D}\symbol{"6B}
\symbol{"4D}\symbol{"6C}
\symbol{"4D}\symbol{"6D}
\symbol{"6E}
\symbol{"6F}
\symbol{"70}
\symbol{"71}
\symbol{"72}
\symbol{"73}
\symbol{"74}
\symbol{"75}
\symbol{"76}
\symbol{"77}
\symbol{"78}
\symbol{"79}
\symbol{"7A}
\symbol{"7B}
}
\newfont{\thairCA}{thair20 scaled\magstep1}
\newfont{\thairzCA}{thairz20 scaled\magstep1}
\newfont{\thaiiCA}{thaii20 scaled\magstep1}
\newfont{\thaibxCA}{thaibx20 scaled\magstep1}
\newfont{\thaibyCA}{thaiby20 scaled\magstep1}
\newfont{\thaibzCA}{thaibz20 scaled\magstep1}

\begin{document}
\sloppy
This is thair at 20 point
{\thairCA\testchars}

This is thairz at 20 point
{\thairzCA\testchars}

This is thaii at 20 point
{\thaiiCA\testchars}

This is thaibx at 20 point
{\thaibxCA\testchars}

This is thaiby at 20 point
{\thaibyCA\testchars}

This is thaibz at 20 point
{\thaibzCA\testchars}

\end{document}