Hi All, I am looking at fitting a new/reconditioned steering rack into my Espace while I am rebuilding it (and no, the job is not very much easier with engine and gearbox removed!!  

 ) 
I have found a few places that supply racks but I have come across 2 different types which are listed as fitting either J8S6/J8SB or J8S7    I have never seen these designations before. 
I can find no reference to these numbers on the oval plate of either of the 2 cars I own.
Can anyone enlighten me and tell me what the difference is please?
Many thanks,
Graham