One Original 22LR magazine with standard 10 round configuration with base pad, follower and spring kit for you to convert. As used by GSG Team UK.
The High Capacity Magazine Upgrade converts your factory 10 round magazine to a 16 round magazine! 

With a round in the chamber and 16 in the mag, that's 17 rounds in the gun (subject to the profile of your ammunition)

The High Capacity Magazine Upgrade replaces the factory plastic base pad and factory follower with an aluminium +3 (Plus 3) base pad and High Capacity Follower.

The +3 basepad is also longer than the factory plastic base pad and allows for more positive seating of the magazine in the gun. 

The extra length is a great feature for 1911 LBP pistols with magazine wells where seating a flush magazine can be difficult. 

Additionally the aluminium construction is more durable than factory plastic base pads making your magazine less prone to breakage upon dropping.

 
Also available as individual components.