How many loose or missing frog bolts are considered a defect by the FRA?

The determination of defects regarding frog bolts, as outlined by the FRA, establishes that the presence of loose or missing frog bolts is only a concern if it reaches a specific threshold. The criteria specify that having none of the bolts missing means that no defect is present. The focus here is on the condition of the frog, which is a vital component of track switches. If there are no loose or missing bolts, the integrity of the frog is maintained, ensuring proper function and safety on the rail line. Thus, the absence of defects in this context denotes that no frog bolts are missing, and the structure is deemed safe for operation.

In relation to the other options, stating that only one bolt being a defect would imply an overly cautious standard. Meanwhile, defining two or more missing bolts as a defect does not align with the FRA's criteria, as it overlooks the importance of having at least one bolt intact. As for any missing bolt being categorized as a defect, this would also fail to reflect the established norms where only a complete absence of bolts would raise concerns. Therefore, the interpretation of having none as a defect aligns with the regulatory guidelines set forth by the FRA.