A loading unit includes a shell assembly and a locking collar. The shell assembly has an annular ring that defines a locking slot and a proximal opening. The proximal opening configured to receive a distal end portion of the surgical instrument. The locking collar is rotatably disposed about the annular ring. The locking collar has a body including a flexible tab that has an inwardly extending lock. The locking collar is moveable about the annular ring between a locked and unlocked configuration. In the locked configuration, the lock passes through the locking slot and into the proximal opening of the annular ring. In the unlocked configuration, the body of the locking collar is rotated about the annular ring from the locked configuration to move the lock from within the proximal opening.