Print all the parts as laid out in the STL's. Make sure your printer is well tuned because of all the threads. I used my prusa MK4 with a 0.4mm nozzle and a 0.15mm layer height and everything came together without any issues. Make sure that you use support when this is needed.
Build instructions
Put the ‘ball’ in the ‘body’, the ball has a hole on one side. Make sure this hole is at the underside of the body.
Screw in the ‘set bolt’ at the underside of the ‘body’, make sure the round top of the set bolt is the hole of the ball.
Put the ‘seat’ in the ‘reducing ring’
Screw the reducing ring and seat into the body
Put the ‘bonnet bolt' into the ‘bonnet’
Put the ‘stem’ into the ‘bonnet’, there is a 90 degree cut out in the bonnet where the stem needs to be in. This requires a little bit of force to put in.
Put this subassembly on to the body, make sure the stem falls into the cutout of the ball.
Tighten the bonnet bolt by using a flat head screw driver.
Screw the flange into the reducing ring
Screw in the reducing ring, flange and seat at the other side of the body.
Screw the bonnet seal into the bonnet
Screw one nut onto the stem put the handle on the first nut, now screw the second nut on top of the handle.