Nintendo Switch Joy-Con comfort grip for single controller
A palm-filling grip that a single Joy-Con slides onto for sideways two-player sessions in Mario Kart or Smash. The Joy-Con body is 102 x 35.9 x 28.4 mm with a dovetail rail on its inner face, so the grip carries a matching 10 mm rail with 0.2 mm clearance and a small lock lip at the top that clicks against the release button. Two rounded handles extend 60 mm below the controller with a 32 mm diameter to mimic the Pro Controller, and a cutout leaves the SL and SR shoulder buttons and the strap rail fully exposed. Print it rail-up with 2.4 mm walls so the dovetail comes out crisp.
Third-party grips are either too loose or scratch the rail. With SpeakCAD you describe the rail fit you want and the handle size for your hands, check the model in the browser without spending anything, and adjust the clearance in the chat before downloading the STL.
Model a Joy-Con comfort grip 130 mm tall with a 102 mm dovetail channel 10 mm wide and 0.2 mm clearance for a Nintendo Switch Joy-Con, a top lock lip 2 mm tall, two 32 mm diameter handles 60 mm long angled 12 degrees outward, and 2.4 mm walls.