Note from Wolff on G21:
When replacing the springs in your hi-capacity 13 round Glock Model 21, .45 ACP magazines, W. C. Wolff Company strongly urges you to obtain Glock part #5397 which is a new base pad locking plate and magazine spring guide if your magazine does not have this part. If you have an early model 21 magazine base pad locking plate which does not have spring supports on each side to support the spring as it compresses then we urge you to obtain this part. The purpose of this part is to help center and supports the magazine spring in the center of the magazine tube as it compresses to reduce the possibility of the magazine spring folding over and locking together rendering the magazine and pistol inoperative. W. C. Wolff company does not recommend +2 magazine extensions for the Glock 21.