Hello Kane,
Thank you for your feedback.
Because when we received the order for FM-103609Y, the drawing enclosed with the order is FM-103069Y_X0 with drive flange 4.2mm, we followed this one to create our FM-103609Y motor drawing.
Therefore, if the drive flange is changed to 3.5mm in FM-103609Y_A0 drawing, we will modify our drawing and return to you with the updated one.
Best regards,
Ryan