A circlip’s rated thrust load is set by the groove wall in the shaft or bore yielding under the ring’s edge, not by the ring itself breaking.
The ring only has to resist expanding or contracting. The groove wall has to carry the whole thrust on a flat annulus of metal one groove-depth high, and it fails by being crushed rather than cut — the published formulas are compressive yield, not shear. That annulus is exactly π/4×(d²−d₂²), so the rating is area times yield strength and nothing else, which is why a soft or shallow groove is the weak point in most retaining-ring failures.
Once you put a real material in. The published tables assume a groove in 200 N/mm² metal, softer than nearly any shaft, and on that assumption the groove does govern at every one of the 41 standard sizes. Take the groove material to S355 and the ring governs 15 of them — only 4 of the 21 external sizes, but 11 of the 20 internal ones, because the internal ring is the thinner of the pair. A 30 mm bore hands over to the ring at 244 N/mm², barely above mild steel. And in a thin-walled aluminium housing neither number applies: the housing dishes and lets the ring lift out with the groove undamaged.
Estimate with the rule, then check it against the calculator that models it properly.
Open Circlip Calculator →A circlip’s rated thrust load is set by the groove wall in the shaft or bore yielding under the ring’s edge, not by the ring itself breaking. The ring only has to resist expanding or contracting.