A circlip retains an axially-loaded part by seating in a groove machined into a shaft or bore. Two dimensions matter above all: the groove diameter, which sets how deep the groove is cut, and the groove width, which sets how much the ring can float. Get either wrong and the ring either can't seat properly or doesn't hold as much axial load as the catalogue rating assumes.
A 25 mm shaft takes a DIN 471 external circlip with a groove diameter of 23.9 mm — 1.1 mm deep — rated for about 7.0 kN of groove strength and 16.2 kN of circlip strength. The lower of the two numbers, groove strength, is what actually limits the joint.
Groove strength (Fₙ) is how much load the shaft or bore material around the groove can take before it deforms. Circlip strength (Fᵣ) is how much the ring itself can take before it deforms or pops out. The joint is only as strong as whichever number is lower — almost always the groove.
If the groove sits on the outside of a shaft, protruding outward to stop something sliding off the end, that's external (DIN 471). If the groove sits inside a bore or housing, protruding inward to stop something sliding out, that's internal (DIN 472). The nominal size always matches the shaft or bore diameter at the groove — not the diameter of whatever part is being retained.
Yes — the load figures here assume a sharp-edged groove corner. Adding a chamfer or radius (often done to avoid stress concentration or ease assembly) measurably reduces the effective retention capacity. For a load-critical joint, that reduction needs to come from the manufacturer's own data, not a general table.
No — groove diameter, width and depth are all matched to the specific nominal size. A circlip sized for a different shaft either won't seat correctly or won't develop its rated spring force in the wrong groove, undermining the whole retention mechanism.