What is this?

Last time, I (poorly) explained that using hand size 12 and 7 for the upstream and downstream inserters respectively lets us fill one lane of a blue belt with only two inserters, but for some reason, this only works when the inserters are placing items within the same transport line segment .

Which was a pretty annoying limitation because inserters cut the transport line 3 meters downstream from their insertion point, which really restricts any designs that try to use the "12 and 7" trick.

Afterwards, I discovered that hand size 11 and 7 also works, and doesn't have this limitation! Actually I already put this to use in a different post, but now I'm properly announcing the "11 and 7" discovery. Or rediscovery...…