Assemblies as disclosed herein for making superhard products by HPHT process comprise a first can portion for accommodating a mixture of materials therein and a second can mated with the first can portion. A leak-tight seal is provided between the first can portion and second can portion in a manner that accommodates the manufacture of relatively longer superhard products without having to change other elements or members used for HPHT processing to thereby provide improved manufacturing flexibility and cost efficiency.