steering wheel fitment

[shnozz]

nobody has been able to flog me a second hand wheel so looks as though i will have to buy a new Momo or Sparco. Before I do, do I need to specify any size in relation to the attachment to the car? silly question maybe but I read somewhere about different size mountings or shapes? Having taken the centre cap off my cirrent wheel there is the central nut and bolt and 3 bolts around this in a triangular format?