I have Shimano PD-M515's on two bikes and the spindle/bearing assembly that threads into the body does not have a hex but a multi splined plastic head. Shimano sold a specific tool, TL-PD40, to remove them. It's just a plastic ring with mating splines inside and can be turned by hand. IIRC, it cost less than $5. Note that on the M515's the left pedal's spindle assembly is left-handed threaded just like the crank threads.