^ That's what I'm thinking too. In 25 years and dozens of trucks and prolly 500kmi of towing something I've never had a hitch pin not fit through the hitch.
If your hitch receiver isn't drilled square it will bend every pin you put in it. And forces exaggerated by the slop between bearing surfaces when using an adapters.
Remember hitch pins are only designed for their recommended strength in shear.
If you introduce any bending forces that little 5/8 pin would need to be significantly larger diameter to not suffer any plastic deformation.