I don't know the 620 personally but I'll share a tip I was given years ago for castle nuts, when you want to have them tight and not really back off. Tighten it and if the pin lines up, you're good, if it needs to go a little more to line up, but you don't want to strip anything, file the backside of the nut a little bit, try it, and repeat as necessary until it lines up at a torque you're comfortable with
Brandon
