2005 s40 front hub
 

I just got a 2005 s40 and need to replace the front wheel bearning. My question is are they a press on or bolt on style?

It's a press-in bearing assembly. This means that though the unit indeed contains the hub and wheel bearing pre-assembled, it still must be pressed into the knuckle as an assembly. Here's the link to Federal Mogul's part for your application sold at Advance AutoParts. I wouldn't necessarily recommend this particular part but it's a good way to see images of what you're looking for and how it's installed. I would definitely recommend OEM, Timken or SKF brands more so. (Trivia: Volvo was originally a division if SKF bearings)

http://shop.advanceautoparts.com/web...4110944&ci_sku=#