Plate O1 is designed as attachment points to connect mechnamical parts at 45??,90?? or 135?? angles. Using it in your mechanical structures, you will have more angle choices.
 
Features:
Can be used to build 45??90??,135?? angles
Three 8mm diameter center holes compatible with 8mm shafts and bearings
Four M4 threaded holes and other M4 mounting holes compatible with most Makeblock components.
Made from aluminum extrusion (high strength), 3mm thick, anodized surface(long time to shelve without barely rusting)