Excellent. By my calculations, 13mm square turns out to be 15.9mm hex wrench, so 16mm (12 pt). It is also exactly 5/8" hex wrench (12 pt).

The ratcheting box end wrench is the neatest thing since ratchet wrenches. I will stop by the pawn shop tomorrow and pick up a 5/8" ratcheting end wrench for a couple bucks.

Thank you very much,

kr