This method won't work as a retrofit to an existing cotter pin installation, but if you're fabricating a new wagon axle or some-such, it's worth considering.
In a typical cotter pin installation. the pin ends up bearing directly against a sometimes-rotating, thrust-bearing element of the assembly, like so.
By giving the cotter pin a collar to fasten, such as a bored-out hex nut, all rotation load is removed from the pin.
The pin only has to secure against a direct thrust (shear) load; any rotation load is borne by the face of the collar.
Note that unless you take extraordinary care with your machining work, you won't end up with a collar that will fit the shaft/pin either way round. Mark the orientation that goes together with a centre punch, to facilitate future disassembly/reassembly.
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