they have a 5-6 & 8mm bore on em, to use the 8mm you use a drill and bail the smaller section.... i have a thread in the dji forum on it..... search "8 & 9 prep"
one other thing i just remembered, the bottoms of suppo have a big aluminum thing with set screws. You gotta drill out your arms for the thing to fit down in. I think it's 3/8" drill, biggest drill usually for the small drill. You also only use 2 of the bolt holes. I've been like that for hundreds of flights, no problems. Almost everybody using bigger motors on dji use only 2 bolts, they put a whimpy motor bolt spacing thing on us