Its called tools3.dat and will be located in the macro folder of the profile you use, for example if you use the standard Mach3Mill profile it will be found in C:\Mach3\macros\Mach3Mill.
Similarly there is one for the offsets, its called fixtures.dat.
Both can be copied over to another drive/computer and it is also a good idea to back them up in case they get corrupted.
Hood