Hurricane front sight

[Geezer]

Last one I fitted involved a combination of my own super-strong superhero fingers and (mostly) a pair of pliers allowing me to open the thing up enough to fit, followed by one of my favourite tools, a light plastic-faced hammer and many gentle taps.

[24voltz]

Well guys thank you for your comments, it's not an easy job but the external circlip pliers (a good pair) got it open enough to ledge it in the groove and a few light taps with the plastic mallet did get it to fully drop in, that won't be coming off any time soon.
But thank you both for your comments.