Size selection for a rod end involves three parameters: bore diameter, thread size, and load rating. Most buyers start with bore and thread. That’s not wrong, but it’s incomplete.
Two rod ends with identical bore and thread dimensions can have load ratings that differ by 40% depending on ball diameter and housing wall thickness. Thread size tells you how it connects. Load rating tells you whether it lasts.
Start with the pin or bolt diameter. The bore of the rod end must match the pin that passes through it. This is a hard constraint. If your clevis pin is 12 mm, your bore is 12 mm.
Match the thread to the rod. Male rod ends thread into a female-threaded component. Female rod ends accept a male-threaded rod or stud. The thread pitch and diameter must match what’s already in your system. For metric applications, M6 through M24 covers most industrial linkage work. For imperial, UNF 1/4 through 3/4 inch covers the equivalent range.
Then verify the load rating. Pull the dynamic load rating (C) from the datasheet, not just the thread size. Your application load divided by the rated C should give a C/P ratio of at least 2.5 for standard oscillating duty. For shock or impact loading, target 3.5 or higher. If the C/P ratio falls below 2, move up one bore size even if the thread still fits.
One thing most sizing guides skip: the thread engagement length matters under bending. If your rod end is taking any moment load at the thread, short engagement lengths cause the shank to act as a lever and fatigue at the thread root. The general rule is a minimum thread engagement of 1.5 times the thread diameter. Check this against your rod design before confirming size.