The 75mm long picatinny rail (dimensions according MIL-STD-1913) is 15mm high to fit on the side of the Stinger 2 magazine body. This height is ideal to fit the arrow quiver right next to the magazine for quick reloading. The 40mm hole distance fits the pre-marked holes (on the inside) of the original Steambow magazine (you need to dismount the magazine body and drill from the inside, there is even a hexagonal recess to hold an M4 nut prepared in the plastic).
The author marked this model as their own original creation.