Update (09/05/2019): this version will work with very minor filing on the edges for clean-up only.
Still working on a final version that can go straight from the printer to the mower. This one needed a little hand filing to get it to operate correctly, e.g. would release when the mower bail was released. I did mow the entire yard with the test version.
Ninja Tek ABS
Update (09/05/2019): See print orientation picture.
Printed these with the top towards the bed, but for future prints I will print it on the side, with the narrow part of the key facing upward, since that one has a slight radius groove.