Originally Posted by
dabac
The crank bolt looks like it could be meant to be a self extracting type. Did you perhaps remove a ring that filled out the gap between the hex head and the crankarm first?
If it was me, I'd try with a regular crank extractor (for square taper) first. Maybe need to use some sort of washer to get the plunger to engage the BB spindle properly. Or swing by your lbs and ask for a self extracting crank bolt ring.
I don't see any pin spanner holes around the bolt so that pretty much eliminates a self-extractor and the threaded shank is too big for a normal square taper so I believe this is an ISIS or similar bottom bracket or a variation on the hollow axle HTII format.