According to gunsholstersandgear.com:

The .22LR Rimfire Conversion Kit is available for the SIG SAUER P220, P226, and P229 models and feature a black hard coat anodized slide, machined from solid aluminum billet. Offered as a complete replacement assembly, the Rimfire Conversion Kit installs as easily as field stripping the pistol. Simply remove the standard slide assembly, install the “new” .22 slide and barrel assembly, and add the included .22LR magazine and you’re ready for the range.