A loading unit assembly includes a shell assembly and a locking collar. The shell assembly has a proximally extending annular ring that defines a cylindrical opening. The annular ring defines a lock opening that passes through the annular ring. The shell assembly defines a retention slot that is adjacent the annular ring on an opposite side of the annular ring from the lock opening. The locking collar is positioned about the annular ring and has a body, a lock, and a retention tab. The body includes a release surface. The locking collar has a locked configuration wherein the lock extends into the cylindrical opening and an unlocked configuration wherein the lock is disposed outwardly of the cylindrical opening. The side of the locking collar opposite the lock is prevented from moving outwardly in relation to the annular ring when the release surface is pressed inwardly towards the annular ring.
