Due to the demand from our customers, FAB Defense has manufactured a new product compatible with the Glock 42, the 42-10 Plus 4 magazine extension for the Glock 42
SUBCOMPACT | .380 AUTO
For those discerning shooters who desired the smallest GLOCK possible, the company responded with the now popular G42 in 380 AUTO with ultra-compact dimensions and easy-to-shoot characteristics. The G42 packs all the features GLOCK customers have come to appreciate - from the GLOCK SAFE ACTION system with its multiple integrated safety features to the brand’s proven reliability and durability." From Glock official website.
Therefore if you are looking to add 4 additional rounds for a total of 10 rounds in a magazine and to get a full grip on the weapon when the magazine is in use, which happens due to the Special ergonomic design that enables secure manipulation of the magazine.
To order the 42-10 go here