I don’ think it is a stretchable arm.
I think they just move the arm forward when you press a button, but you won’t notice it is detached from your body because of the camera position.
I believe you have to make a viewmodel, then you can tween the size of the arm to the wanted length, to get the wanted length you can cast a ray from the middle of camera, torwards were the player is looking at to get a vector3 of were the ray from the camera collides with in the workspace. Then you calculate the distance from camera to the hitpos, then use that distance as the size of the arm, and tween the size of the arm to the magnitude, about the rotation idk hahaha, idk if this will help or if this might not work, but I hope it helps maybe a tiny bit