Ordered my first sex toy. Tips and advice?

Hi,

So I ordered some new silicone (because it is more hygienic and doesn't adapt a certain smell) anal beads, the Fifty Shades of Grey ones: http://www.superdrug.com/medias/sys_...5352179742.jpg

So I'm versatile, but in my relationship I'm more top. I plan to use them for myself and for my boyfriend. Now the thing is that my penis is not big (15/16cm) and not really thick.

My boyfriend doesn't know I ordered it, so how should I introduce it to him in the bedroom? I definitely don't wanna mention it before sex, but just get it out during foreplay. Another thing is I don't want him to get used to the beads as much, because then my penis is not going to be enough for him anymore, and I don't want that to happen.

Any tips, advice? :)

Thanks