What makes you think it would be p505 compatible?
I'm not familiar with the "easton mounting standard". The Magene P505 PM spider is round and has four mounting bolts, not unlike those pictured in this thread (which are apparently compatible). raisinberry777 set me straight. I'm just not that into my p505. I thought having a PM would be the final frontier, but the p505 added 100g+ to my bike, and the data isn't *that* useful.