3 KudoZ points awarded for this answer. Comment: "Thank you, everyone, for a range of possible answers. In the end, and after doing some more research, I was torn between "template" and "guide plate", both of which seemed entirely possible. In the end I have gone with "template" as it yields more google refs., including a number of relevant ones that describe the use of joystick templates in connection with powered wheelchairs, which is a similar situation. While it is good to be reminded that "gate" is used in cars etc., I felt that such gates aren't entirely similar as they permit a whole number of different movements, while the one I am descriving permits side-to-side movement only. "