The GDT font was changed to GD&T for Claris CAD 2.0v3, which was also the first System 7 compatible version. The name was changed due to the fact that there is a company named GDT that produces postscript fonts and drivers
GD&T, which is a collection of frequently used drafting symbols designed to look good when plotted (stroked rather than bitmapped), is not automatically installed with the Claris CAD installer.
To install the font under System 7, simply drop the font onto the System folder an click OK when it asks if you want to put it in the System file. You could also drag it directly onto the System file.
Files that were created with earlier versions of Claris CAD will not have the GD&T font immediately available, and may show the GDT font, which will not be available. To remedy this, go under the Font menu to Fonts... Select Change menu, show the GD&T font and remove the GDT font.