BJCM double type 3 or type 4?

[SuperSue77]

Hi, can anyone help me? I've been reading. Number of posts about the BJCM double and people have been referring to a bjcm 3 or a bjcm 4. I'm confused as to what the difference is and how you can tell. I am planning to buy a bjcm double 2012 but am not sure whether it's a 3 or a 4 and wondering whether I should find out before I buy. But not sure which I'd want anyway as don't know the difference! Can anyone help with this? Thanks.

The 3 and 4 refer to the singles as there is a 3 and a 4 wheeled version. There's only one style of double (apart from the differences depending on the year).

Thanks for your reply, I was getting confused!