The present disclosure relates to an insertion piece for a camshaft phaser and the camshaft phaser. The insertion piece is configured to be partially inserted and mounted into a center hole of the rotor of the camshaft phaser. The insertion piece has a stepped cylindrical shape across its entirety and includes a first cylinder portion, a second cylinder portion, and a third cylinder portion, which are connected to each other and are coaxially arranged. The first cylinder portion extends along the axial direction; the second cylinder portion is located at one axial side of the first cylinder portion and extends along the axial direction; the third cylinder portion is located at one axial side of the second cylinder portion and extends along the axial direction; and a clamping connection portion for fixing the coil spring of the camshaft phaser is formed on the third cylinder portion.