The Summary Owner's Manual starts the lock information on page SM-21 but neglects to continue that information on the next page. Shopsmith will sell you a complete Mark 7 Manual available through the online catalog for $35.99. I do recommend having the manual.
If you have not seen this before - WARNING collecting Shopsmith tools can be addicting, but don't tell your wife and we won't either. Enjoy your tools.
Mark V completely upgraded to Mark 7
Mark V 520
All SPT's & 2 Power Stations
Model 10ER S/N R64000 first one I restored on bench w/ metal ends & retractable casters. Has Speed Changer, Model 4E Jointer, Jig Saw with lamp, a complete set of original accessories & much more.
Model 10E S/N 1077 oldest one I have restored. On bench w/ metal ends & retractable casters.