Does anyone know the socket size to remove the oil filter cap on my 2001 Volvo S40? It's either 86.6mm or 86.4mm

 

You can buy a CTA filter socket (#2489) from IPD or FCP for about $7 plus shipping - FCP simply shows as 86 mm x 16 flute (sides). I'd bet Autozone or Napa have a comparable tool on the shelf as well.

You can also use a smaller size band wrench - there's just enough wiggle room to get the filter off with one of those as well.