This is a segment of NATO-spec STANAG 4694 rail, intended to supercede the 1913 Picatinny rail. The primary feature of the 4694 rail is better tolerances than the 1913, while allowing backwards compatibility with 1913-spec attachments.
The best way to mount an attachment to a 4694 rail is to connect the attachment to the top surface of a rail, and the bottom two angled surfaces, as indicated in the image included.
This is a STEP file meant for use in CAD work. It is possible to 3D print this after a file conversion, but that is not the intended application. If you have questions about integrating this rail into your model, please send me a message on my Twitter.
Bounding Box dimensions: 94.52mm x 21.20mm x 14.40mm LWD
Tongue dimensions: 4.70mm x 3.13mm LD
Groove dimensions: 5.28mm x 3.13mm LD