FYI, those of us who have Gen1-2-3 Glocks and Advantage Arms .22LR converter kits for them. Especially those who have now added a Gen4 Glock. The AA kits used to be interchangeable on all Glock versions. No more. The Gen4 Glock recoil spring system is different on most model Glocks than on Gen1-2-3 Glocks. AA has made a Gen4 .22LR kit for Gen4 Glocks. The new kit is so marked as Gen4 and works as expected. POINT OF POST: If you use an earlier version AA kit on a Gen4 Glock, the misfitting AA recoil spring system will damage the frame plastic just ahead of the front rails. It may also damage the AA recoil spring system. If you hunt up the AA parts site, you will find an AA Gen4 recoil spring assembly that will fit a Gen1-2-3 AA kit so that the older AA kit can be used on a Gen4 Glock. Surprised the hell out of me too. I ordered one for an older LE19-23 kit for which I have Glock Gen2, 3, & 4 guns. By using the corresponding AA recoil spring assembly, the older kit is useable on either old or new Glocks.