Use two M3x8mm countersink screws (spacing: 122mm center-to-center) to mount an Archer A7 onto a pole (35.5mm diameter)!
Snaps firmly onto the pole, but it'll slide down under the router's weight, so you'll need a stop on the pole.
Also provided is the OnShape model, so you can adjust ALL the parameters to your heart's content! Different pole diameters, different hole diameters/spacings, anything!
The author hasn't provided the model origin yet.