This isn't a Pilot RC plane, but something I was working on tonight... reworking the H9 Sukhoi hatch bolts/blindnuts. The stock ones were shot after about 4 flights with the DA-170. They were 3mm and had junk hardwood blocks that just split and broke off... just from vibration. But, the recessed holes for the top of the 3mm bolts really didn't allow for rubber washers. So, anyway, I sanded off what was left of the stock junk hardwood blocks and replaced them with 1/4" aircraft plywood blocks (that I cut with my new tablesaw, haha). I went with 4mm blindnuts and bolts. I also Z-poxied in the recessed holes so I could use large rubber washer/sealing washers. Should hold up nice now, this is the same setup that comes stock on the Pilot RC planes and it has needed no maintenance on those planes as of yet.