Designed around the harsh demands of USPSA and "3-Gun" competition, this extension gives you five rounds of extra capacity. Falls within the 140mm rule when attached to a Mec-Gar Optimum series magazine. This base pad will also fit and function on a CZ SP-01 factory magazine but it extends beyond the 140mm rule. This base pad will not work on most factory metal base-pad magazines without frame modifications. G-Post locking screw makes removing the base pad simple and easy - yet will not "pop off" when dropped.FeaturesAdds five shots in 9mm, four in 40 S&WOptimized for USPSA "Limited" competitionWorks best with extended magazine spring