The 1st Gen pencil Compatible with Apple Ipad Pro better before 2018 version. 1.5mm metal tip.

 It works on iPhone as well. Check the image with model description. 

It doesn't work great on 2018 to 2020 iPad, if you need good experience for 2018 to 2021 iPad,

choose 2nd or 3rd Gen pencil with Palm rejection and with fine tip ,good for drawing and sketching