Unusual Tools: Klein folding rule

An old folding rule made by M. Klein & Sons, better known today for their Klein linesman pliers:

Unlike most other zig-zag rulers which had brass hinges between the ruler sections, the Klein product made use of an ingenious connector consisting of mated male- and female-receptacles, providing for a very positive lock in both closed and opened positions.  A much more sensible design than the Interlox Master Rule featured in a previous blog entry.