A loading unit for engagement with a surgical instrument, and including single and double retention slots. At least one single retention cavity includes a first retention guiding surface configured to engage a first pusher guiding surface of a single pusher retained therein, a second retention guiding surface configured to engage a second pusher guiding surface of a single pusher retained therein, a third retention guiding surface configured to engage a third pusher guiding surface of a single pusher retained therein, and a fourth retention guiding surface configured to engage a fourth pusher guiding surface a the single pusher retained therein. At least one double retention cavity includes a first retention guiding surface configured to engage a first pusher guiding surface of a double pusher retained therein, and a second retention guiding surface configured to engage a second pusher guiding surface of a double pusher retained therein.
