A stapling surgical instrument and a loading unit

A stapling surgical instrument comprising a shaft assembly (20) and a loading unit (30);

• wherein the shaft assembly (20) comprises a main body (221), a firing rod (23), and a sensing collar (24), the main body (221) surrounds the sensing collar (24), the sensing collar (24) surrounds the firing rod (23) directly, the firing rod (23) is aligned with a longitudinal axis, and a distal end of the main body (221) is provided with a notch (2212);
• the loading unit (30) comprises an insertion portion (36), the insertion portion (36) is provided with a mounting boss (311), a first lumen (3101), and a second lumen (3102), a proximal end of the insertion portion (36) and the mounting boss (311) are spaced apart by a first distance along the longitudinal axis, the first lumen (3101) and the second lumen (3102) are configured to intersect with each other;
• when the loading unit (30) is configured to be releasably mounted to the shaft assembly (20), the insertion portion (36) is inserted into the notch (2212), the second lumen (3102) is provided with a second dimension to accommodate a distal end of the firing rod (23) and a distal end of the sensing collar (24), and the first lumen (3101) is provided with a first dimension to accommodate the distal end of the firing rod (23).