What feature indicates a left-handed thread on the brass barrel of a turnbuckle?

A left-handed thread on the brass barrel of a turnbuckle is indicated by a groove. This feature is significant because it allows for easy identification of the threading direction. In applications where turnbuckles are used, it's crucial to distinguish between left-handed and right-handed threads to ensure proper assembly and functionality. The groove serves as a visual cue to the user, preventing any potential errors during installation or adjustment.

Color coding is not typically used in this context, as it can be subjective and not as universally recognized. Engraved markings could provide information about the thread type, but they may not be as immediately noticeable or specific for distinguishing left-handed from right-handed threads as a groove. A ball detent relates to mechanisms that hold parts in place and is not relevant to indicating thread direction. The groove is thus the most effective and recognized means to identify left-handed threads in turnbuckle designs.