Flapper Wing Drive Link
This straight dog-bone link is part of the 'SG90 Scotch-Yoke Flapping Wing Rig' kit, and you print two. It is 46 x 9 x 4.4 mm, with 3.4 mm M3 clearance holes 37.0 mm apart in 9 mm bosses on an 8 mm wide, 4.0 mm stack. The lower end takes an M3x10 into the slider's heat-set insert. The upper end takes an M3x16 with a nyloc through the rocker. Each end has a 6.5 mm, 0.4 mm tall washer ring on opposite faces, so only the rings rub against the slider and the rocker. The whole stack is 4.4 mm and fits the 4.5 mm gap between them.
mechanism kit sg90 linkage