The parts were purchased from a US supplier of precision balls with a very good reputation.
We were involved in supplying people who make bearings, in China. Big bearings, 3 meters. Guy who spent several months with us was in fact the plant manager for a very well-known US manufacturer of bearings. So tit for tat (and I keep a few in reserve):
Problem came up with their bearings. Helicopters falling out of the sky size problem. So they put together a group to figure out why. Start at A, go to B, C, D.
At one point they found that an accounting decision had been made to change suppliers for certain stainless steel balls. Off to the supplier's shop to investigate.
Multiple engineers in the minivan, everything looked hunky-dory except our buddy the factory guy wasn't happy. He had realworld experience making parts. The subzero freezer was nowhere near big enough to cryo the volume of balls they'd been shipping.
End of story, obviously they hadn't froze those balls long enough or some of them at all. In service they'd heat up, expand in a way they weren't supposed to, and seize the bearing, which had a negative effect on the flight characteristics. Them rotors are supposed to keep turning no matter what.
All of this by US companies in the continental United States, no parts from Roosha, China, Zimbabwe, or Mexico.
Hence, US-made parts are shit ?
I bet anyone who has been in any kind of industry anywhere has similar stories. In fact I was just reading one about cycloidal teeth and detonators for WW II bombs and such. Total fuckup. USA, top to bottom.
When I first started out I was perfect but after a few errors here and there, I've become slower to smarm at other people.