Needle protector assemblies including needle assemblies and needle protectors for housing used blood collection needles are disclosed. The needle protectors are single-piece protectors that include an open distal end for receiving a needle hub (with a needle mounted thereon). A retaining member locks the needle hub when the needle hub is substantially retracted. A stop engages the needle hub in a fully retracted position such that a needle post is completely contained within an interior chamber of the needle protectors. A viewing slot in the needle protectors is provided.