Hi taytam176,
Thank you for reaching out Microsoft Community,
The Surface Slim Pen works on Surface Pro 7 but the Surface Pro X Signature Typecover will not work on other Surface Pros because it uses mechanical and electrical fangs to get it connected to the Surface Pro X unlike other Surface Pro devices wherein its designed typecover uses pins (magnetic pins) to establish connection between the tablet and the removable keyboard.
If this answers your question, feel free to mark this post as an answer. Otherwise, don't hesitate to respond to this thread if you need further assistance.
Kind Regards,
Crest_Z