Help with aftermarket steering wheel. Images included.

[P1E]

I purchased an aftermarket (second hand) steering wheel a couple of weeks ago and I cannot work out how to fit it to my R33 GTS25-t.

I managed to remove the standard steering wheel without much hassle:

This is the aftermarket steering wheel and boss kit:

Now, when I try to fit the boss kit...

... it doesn't fit. Have I missed a step? Does something else need to come out or go in? Or have I been given the incorrect boss kit? If this is the case, how can I find out what vehicle this boss kit actually suits (so that I can sell it) and where can I purchase a boss kit to fit my R33 GTS25-t?

Thank-you!

[xRHETTx]

It looks like the correct boss kit, very similar to mine.

Does the boss kit just not fit on the spline? Its a taper fit, so it might be pretty hard to get on, just jiggle it around a bit?