Original so-called “Knee” mortar used by the Japanese in WWII.  This piece is in mint condition with low, matching numbers throughout. This piece was demilitarized correctly by the cutting of a 3 inch diameter hole in the receiver, rendering it inoperable.  What makes this piece extraordinary is not the exceptional preservation of the metal, but the presence of the fragile canvas spring cover, and the leather pull-tab, which I have actually never seen.  The cloth storage bag is an old reproduction.  If you want the best that history has to offer, this piece is not upgradable!