The System I Stringlock has three sections, each of which locks two strings in a clamp-like manner with vertical pressure between the bottom of the lock blocks and the main frame of the nut lock. This is identicle in function to the Kahler_stringlock of the same era. The Kahler stringlock can be used in retrofit of this hard to find system I stringlock if it is completely missing.  The Kahler 5513 has the same window size for the strings and is slightly larger to cover the old screw holes. The old mounting screw pattern is slightly different but will be covered. It's a great retrofit.

If you want to replace some parts of your system I stringlock you will want a rebuild kit. It contains 3 clamp plates, 3 clamp screws and allen wrench and 4 stringlock mounting screws. These are all the parts minus the actual base piece. $18.00