Scott, when you said the 6mm bolt you probably ment allen head size? Is so the thread is M8. Now if it is fine thread M8x1, the helicoil insert outside diameter before insertion would be 10.25mm. The tap for it would have a major diameter 9.422mm. If it is coarse thread M8x1.25 (unlikely) you need even more clearance in the head hole. Check this hole to make sure you have clearance!
Reg. Mike