It's a cassette freehub. 36T big cog, 32 spokes. 20" wheel.

The 47T capacity of the RD is already too low for the drivetrain (wide range 3x10). The chain will fall slack on the small half of the cassette when the front is in the granny ring. We thought about going to a mid-length RD, but then there wouldn't be any ratio overlap between the granny ring and the middle ring before the chain went slack.