USAG 6mm (9/32") Roller Type Stud Driver Set - popular size for European head/exhaust studs. I've also run across these in HVAC applications (in radiant heat manifolds).

These tools (Facom 287B Series or USAG 459/1 Series...the 2 are identical) are the best and most compact stud extractors I've ever used. Studs are gripped in either direction (ie, the tools can be used to remove or install studs) by 3 sets of rollers (see photo) . 1/2" drive for plenty of torque. I stock these USAG version of this tool as it's less expensive than Facom and comes with a US warranty.