LEGO® Technic review: 42145 Airbus H175 Rescue Helicopter | New Elementary: LEGO® parts, sets and techniques
gears - What are the dimensions of a technic axle? - Bricks
Build useful stuff with Lego — HackSpace magazine
LEGO Design
What is the interference lock offset of a LEGO stud/hole such that it fits snugly into another piece? (i.e. What are the snap mechanism dimensions?) - Quora
LEGO part 85489b - Red Train Wheel RC Train, Spoked with Technic Axle Hole and Counterweight, 37 mm diameter (Flanged Driver) at BrickScout